Architectural mode configuration

ABSTRACT

A determination is made that a configuration architectural mode facility is installed in a computing environment that is configured for a plurality of architectural modes and has a defined power-on sequence that is to power-on the computing environment in one architectural mode of the plurality of architectural modes. Based on determining that the configuration architectural mode facility is installed, the computing environment is reconfigured to restrict use of the one architectural mode. The reconfiguring includes selecting a different power-on sequence to power-on the computing environment in another architectural mode of the plurality of architectural modes, wherein the another architectural mode is different from the one architectural mode, and executing the different power-on sequence to power-on the computing environment in the another architectural mode in place of the one architectural mode restricting use of the one architectural mode.

This application is a continuation of co-pending U.S. patent applicationSer. No. 15/401,693, entitled “ARCHITECTURAL MODE CONFIGURATION,” filedJan. 9, 2017, which is a continuation of U.S. Pat. No. 9,582,295,entitled “ARCHITECTURAL MODE CONFIGURATION,” issued Feb. 28, 2017, eachof which is hereby incorporated herein by reference in its entirety.

BACKGROUND

One or more aspects relate, in general, to configurations of computingenvironments, and in particular, to altering the configurations of suchenvironments.

Computing environments offer a range of capabilities and functionsdepending on the architectural configurations of the environments. Twoarchitectures that have been offered by International Business MachinesCorporation, Armonk, N.Y., include ESA/390 and z/Architecture.

ESA/390 is a predecessor architecture to z/Architecture. However, whenz/Architecture was introduced, ESA/390 continued to be supported. Tosupport both architectures in one environment, certain procedures arefollowed. For instance, in power-up, ESA/390 is booted, and then, aswitch may be made to the z/Architecture, if desired. This allowedlegacy software to continue executing without a change. Other suchprocedures are provided in order to support both architecturalconfigurations in one environment.

SUMMARY

Shortcomings of the prior art are overcome and advantages are providedthrough the provision of a computer program product for reconfiguring acomputing environment. The computer program product includes, forinstance, a computer readable storage medium readable by a processingcircuit and storing instructions for execution by the processing circuitfor performing a method. The method includes, for instance, determiningthat a configuration architectural mode facility is installed in acomputing environment that is configured for a plurality ofarchitectural modes and has a defined power-on sequence that is topower-on the computing environment in one architectural mode of theplurality of architectural modes, the one architectural mode comprisinga first instruction set architecture and having a first set of supportedfeatures. Based on determining that the configuration architectural modefacility is installed, the computing environment is reconfigured torestrict use of the one architectural mode. The reconfiguring includes:selecting a different power-on sequence to power-on the computingenvironment in another architectural mode of the plurality ofarchitectural modes, wherein the other architectural mode is differentfrom the one architectural mode, and the other architectural modeincludes a second instruction set architecture and having a second setof supported features; and executing the different power-on sequence topower-on the computing environment in the other architectural mode inplace of the one architectural mode restricting use of the onearchitectural mode.

Methods and systems relating to one or more embodiments are alsodescribed and may be claimed herein. Further, services relating to oneor more embodiments are also described and may be claimed herein.

Additional features and advantages are realized. Other embodiments andaspects are described in detail herein and are considered a part of theclaimed invention.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more aspects are particularly pointed out and distinctly claimedas examples in the claims at the conclusion of the specification. Theforegoing and other objects, features, and advantages are apparent fromthe following detailed description taken in conjunction with theaccompanying drawings in which:

FIG. 1A depicts one example of a computing environment to incorporateand use one or more aspects of a configuration architectural modefacility;

FIG. 1B depicts one example of a virtual computing environment toincorporate and use one or more aspects of a configuration architecturalmode facility;

FIG. 2 depicts another example of a computing environment to incorporateand use one or more aspects of a configuration architectural modefacility;

FIG. 3A depicts yet another example of a computing environment toincorporate and use one or more aspects of a configuration architecturalmode facility;

FIG. 3B depicts further details of the memory of FIG. 3A;

FIG. 4A depicts one embodiment of the logic to power-on a computingenvironment in one architectural mode;

FIG. 4B depicts one embodiment of further processing associated with thepower-on process of FIG. 4A;

FIG. 5 depicts one embodiment of a format of a program status word;

FIG. 6A depicts one embodiment of the logic to power-on a computingenvironment in an architectural mode different from the onearchitectural mode powered-on in FIG. 4A;

FIG. 6B depicts one embodiment of further processing associated with thepower-on process of FIG. 6A;

FIG. 7 depicts one example of a format of a Load Program Status Wordinstruction;

FIG. 8A depicts one example of a format of a Signal Processorinstruction;

FIG. 8B depicts one embodiment of processing associated with the SignalProcessor instruction of FIG. 8A;

FIG. 9 depicts one embodiment of the logic to power-on a computingenvironment in a reconfigured configuration;

FIG. 10 depicts further changes to be made in reconfiguring a computingenvironment;

FIG. 11 depicts one embodiment of the logic to reset a computingenvironment;

FIG. 12 depicts one embodiment of logic to configure a computingenvironment;

FIG. 13 depicts one embodiment of a computer program product;

FIG. 14 depicts one embodiment of a host computer system;

FIG. 15 depicts a further example of a computer system;

FIG. 16 depicts another example of a computer system comprising acomputer network;

FIG. 17 depicts one embodiment of various elements of a computer system;

FIG. 18A depicts one embodiment of the execution unit of the computersystem of FIG. 17;

FIG. 18B depicts one embodiment of the branch unit of the computersystem of FIG. 17;

FIG. 18C depicts one embodiment of the load/store unit of the computersystem of FIG. 17;

FIG. 19 depicts one embodiment of an emulated host computer system;

FIG. 20 depicts one embodiment of a cloud computing node;

FIG. 21 depicts on embodiment of a cloud computing environment; and

FIG. 22 depicts one example of abstraction model layers.

DETAILED DESCRIPTION

In accordance with one aspect, a capability is provided that restrictsuse of a configuration by a computing environment configured to supportmultiple configurations, such that one or more aspects of the restrictedconfiguration are unavailable for use. As one example, a processor isconfigured in a configuration architectural mode (CAM). In CAM, acomputing environment (e.g., a processor, a logical partition, a guest),which is originally configured for a plurality of architectures, e.g., alegacy architecture and an enhanced architecture, is re-configured suchthat one or more aspects of at least one of the architectures, such asthe legacy architecture, is no longer supported. In such aconfiguration, the unsupported aspects of the architecture are notavailable.

As one particular example, a Configuration z/Architecture ArchitecturalMode (CZAM) facility is provided in computing environments that supportmultiple architectures, such as ESA/390 and z/Architecture, whichremoves the ability to use aspects of ESA/390. Instead, z/Architecture(and/or other architectures, in other embodiments other than ESA/390) isused. CZAM may apply to a native machine, a logical partition, and/or avirtual guest, as examples.

One example of a computing environment to incorporate and use one ormore aspects of the configuration architectural mode facility isdescribed with reference to FIG. 1A. Referring to FIG. 1A, in oneexample, a computing environment 100 is based on the z/Architecture,offered by International Business Machines (IBM®) Corporation, Armonk,N.Y. The z/Architecture is described in an IBM Publication entitled“z/Architecture—Principles of Operation,” Publication No. SA22-7932-09,10^(th) Edition, September 2012, which is hereby incorporated byreference herein in its entirety. Although the computing environment isbased on the z/Architecture, in one embodiment, it also supports one ormore other architectural configurations, such as ESA/390.

Z/ARCHITECTURE, IBM, Z/VM and Z/OS (referenced below) are registeredtrademarks of International Business Machines Corporation, Armonk, N.Y.Other names used herein may be registered trademarks, trademarks orproduct names of International Business Machines Corporation or othercompanies.

As one example, computing environment 100 includes a central processorcomplex (CPC) 102 coupled to one or more input/output (I/O) devices 106via one or more control units 108. Central processor complex 102includes, for instance, a processor memory 104 (a.k.a., main memory,main storage, central storage) coupled to one or more central processors(a.k.a., central processing units (CPUs)) 110, and an input/outputsubsystem 111, each of which is described below.

Processor memory 104 includes, for example, one or more partitions 112(e.g., logical partitions), and processor firmware 113, which includes alogical partition hypervisor 114 and other processor firmware 115. Oneexample of logical partition hypervisor 114 is the ProcessorResource/System Manager (PR/SM), offered by International BusinessMachines Corporation, Armonk, N.Y.

A logical partition functions as a separate system and has one or moreapplications 120, and optionally, a resident operating system 122therein, which may differ for each logical partition. In one embodiment,the operating system is the z/OS operating system, the z/VM operatingsystem, the z/Linux operating system, or the TPF operating system,offered by International Business Machines Corporation, Armonk, N.Y.Logical partitions 112 are managed by logical partition hypervisor 114,which is implemented by firmware running on processors 110. As usedherein, firmware includes, e.g., the microcode and/or millicode of theprocessor. It includes, for instance, the hardware-level instructionsand/or data structures used in implementation of higher level machinecode. In one embodiment, it includes, for instance, proprietary codethat is typically delivered as microcode that includes trusted softwareor microcode specific to the underlying hardware and controls operatingsystem access to the system hardware.

Central processors 110 are physical processor resources allocated to thelogical partitions. In particular, each logical partition 112 has one ormore logical processors, each of which represents all or a share of aphysical processor 110 allocated to the partition. The logicalprocessors of a particular partition 112 may be either dedicated to thepartition, so that the underlying processor resource 110 is reserved forthat partition; or shared with another partition, so that the underlyingprocessor resource is potentially available to another partition. In oneexample, one or more of the CPUs include aspects of a configurationarchitectural mode facility 130 described herein.

Input/output subsystem 111 directs the flow of information betweeninput/output devices 106 and main storage 104. It is coupled to thecentral processing complex, in that it can be a part of the centralprocessing complex or separate therefrom. The I/O subsystem relieves thecentral processors of the task of communicating directly with theinput/output devices and permits data processing to proceed concurrentlywith input/output processing. To provide communications, the I/Osubsystem employs I/O communications adapters. There are various typesof communications adapters including, for instance, channels, I/Oadapters, PCI cards, Ethernet cards, Small Computer Storage Interface(SCSI) cards, etc. In the particular example described herein, the I/Ocommunications adapters are channels, and therefore, the I/O subsystemis referred to herein as a channel subsystem. However, this is only oneexample. Other types of I/O subsystems can be used.

The I/O subsystem uses one or more input/output paths as communicationlinks in managing the flow of information to or from input/outputdevices 106. In this particular example, these paths are called channelpaths, since the communication adapters are channels.

Another example of a computing environment to incorporate and use one ormore aspects of the CAM facility is described with reference to FIG. 1B.In this example, a computing environment 150 includes a centralprocessor complex 152 providing virtual machine support. CPC 152 iscoupled to one or more input/output (I/O) devices 106 via one or morecontrol units 108. Central processor complex 152 includes, for instance,a processor memory 154 (a.k.a., main memory, main storage, centralstorage) coupled to one or more central processors (a.k.a., centralprocessing units (CPUs)) 110, and an input/output subsystem 111.

Processor memory 154 includes, for example, one or more virtual machines162, and processor firmware 163, which includes a host hypervisor 164and other processor firmware 165. One example of host hypervisor 164 isz/VM®, offered by International Business Machines Corporation, Armonk,N.Y.

The virtual machine support of the CPC provides the ability to operatelarge numbers of virtual machines 162, each capable of hosting a guestoperating system 172, such as Linux. Each virtual machine 162 is capableof functioning as a separate system. That is, each virtual machine canbe independently reset, host a guest operating system, and operate withdifferent programs 120. An operating system or application programrunning in a virtual machine appears to have access to a full andcomplete system, but in reality, only a portion of it is available.

In this particular example, the model of virtual machines is a V=Vmodel, in which the absolute or real memory of a virtual machine isbacked by host virtual memory, instead of real or absolute memory. Eachvirtual machine has a virtual linear memory space. The physicalresources are owned by host 164, and the shared physical resources aredispatched by the host to the guest operating systems, as needed, tomeet their processing demands. This V=V virtual machine (i.e., pageableguest) model assumes that the interactions between the guest operatingsystems and the physical shared machine resources are controlled by thehost, since the large number of guests typically precludes the host fromsimply partitioning and assigning the hardware resources to theconfigured guests. One or more aspects of a V=V model are furtherdescribed in an IBM® publication entitled “z/VM: Running Guest OperatingSystems,” IBM® Publication No. SC24-5997-02, October 2001, which ishereby incorporated by reference herein in its entirety.

Central processors 110 are physical processor resources that areassignable to a virtual machine. For instance, virtual machine 162includes one or more logical processors, each of which represents all ora share of a physical processor resource 110 that may be dynamicallyallocated to the virtual machine. Virtual machines 162 are managed byhost 164.

In one embodiment, the host (e.g., z/VM®) and processor (e.g., System z)hardware/firmware interact with each other in a controlled cooperativemanner in order to process V=V guest operating system operations withoutrequiring transfer of control from/to the guest operating system and thehost. Guest operations can be executed directly without hostintervention via a facility that allows instructions to beinterpretively executed for a pageable storage mode guest. This facilityprovides an instruction, Start Interpretive Execution (SIE), which thehost can issue, designating a control block called a state descriptionwhich holds guest (virtual machine) state and controls, such asexecution controls and mode controls. The instruction places the machineinto an interpretive-execution mode in which guest instructions andinterruptions are processed directly, until a condition requiring hostattention arises. When such a condition occurs, interpretive executionis ended, and either a host interruption is presented, or the SIEinstruction completes storing details of the condition encountered; thislatter action is called interception. One example of interpretiveexecution is described in System/370 Extended Architecture/InterpretiveExecution, IBM Publication No. SA22-7095-01, September 1985, which ishereby incorporated by reference herein in its entirety.

In particular, in one embodiment, the interpretative execution facilityprovides an instruction for the execution of virtual machines. Thisinstruction, called Start Interpretative Execution (SIE), is issued by ahost which establishes a guest execution environment. The host is thecontrol program directly managing the real machine and a guest refers toany virtual or interpreted machine. The machine is placed in theinterpretative execution mode by the host, which issues the SIEinstruction. In this mode, the machine provides the functions of aselected architecture (e.g., z/Architecture, ESA/390). The functionsinclude, for instance, execution of privileged and problem programinstructions, address translation, interruption handling, and timingamong other things. The machine is said to interpret the functions thatit executes in the context of the virtual machine.

The SIE instruction has an operand, called the state description, whichincludes information relevant to the current state of the guest. Whenexecution of SIE ends, information representing the state of the guest,including the guest PSW is saved in the state description before controlis returned to the host.

The interpretative execution architecture provides a storage mode forabsolute storage referred to as a pageable storage mode. In pageablestorage mode, dynamic address translation at the host level is used tomap guest main storage. The host has the ability to scatter the realstorage of pageable storage mode guests to usable frames anywhere inhost real storage by using the host DAT, and to page guest data out toauxiliary storage. This technique provides flexibility when allocatingreal machine resources while preserving the expected appearance of acontiguous range of absolute storage for the guest.

A virtual machine environment may call for application of DAT twice:first at the guest level, to translate a guest virtual address throughguest managed translation tables into a guest real address, and then,for a pageable guest, at the host level, to translate the correspondinghost virtual address to a host real address.

In certain cases, the host is to intercede in operations normallydelegated to the machine. For this purpose, the state descriptionincludes controls settable by the host to “trap,” or intercept, specificconditions. Interception control bits request that the machine returncontrol to host simulation when particular guest instructions areencountered. Intervention controls capture the introduction of anenabled state into the PSW, so that the host can present an interruptionwhich it holds pending for the guest. Intervention controls may be setasynchronously by the host on another real processor whileinterpretation proceeds. The machine periodically refetches the controlsfrom storage, so that updated values will be recognized. Guestinterruptions can thereby be made pending without prematurely disturbinginterpretation.

In one embodiment, mode controls in the state description specifywhether the guest is executed in the ESA/390 or z/Architecture mode andselects one of a plurality of ways to represent guest main storage of aguest virtual machine in host storage. In accordance with oneembodiment, a control bit is provided in a state control to selectbetween a guest in a first and a second architectural mode (e.g.,z/Architecture and ESA/390, respectively). In accordance with anotherembodiment, two distinct instructions may provide a host with theability to create a first and a second guest virtual machine, e.g.,distinct instructions SIEz and SIEe may be provided to start guestmachines in a z/Architecture and ESA/390 mode, respectively.

The SIE instruction runs a virtual server dispatched by the controlprogram until the server's time slice has been consumed or until theserver wants to perform an operation that the hardware cannot virtualizeor for which the control program is to regain control. At that point,the SIE instruction ends and control is returned to the control program,which either simulates the instruction or places the virtual server inan involuntary wait state. When complete, the control program againschedules the virtual server to run, and the cycle starts again. In thisway, the full capabilities and speed of the CPU are available to thevirtual server. Only those privileged instructions that requireassistance from or validation by the control program are intercepted.These SIE intercepts, as they are known as, are also used by the controlprogram to impose limits on the operations a virtual server may performon a real device.

Further details regarding SIE are described in ESA/390interpretive-execution architecture, foundation for VM/ESA, Osisek etal., IBM Systems Journal, Vol. 30, No. 1, January 1991, pp. 34-51, whichis hereby incorporated by reference herein in its entirety.

Another example of a computing environment to incorporate and use one ormore aspects of the configuration architectural mode facility isdescribed with reference to FIG. 2. In this example, a computingenvironment 200 includes a non-partitioned environment that isconfigured for a plurality of architectural modes, including thez/Architecture and ESA/390. It includes, e.g., a processor (centralprocessing unit—CPU) 202 that includes, for instance, a configurationarchitecture mode facility 204, and one or more caches 206. Processor202 is communicatively coupled to a memory portion 208 having one ormore caches 210, and to an input/output (I/O) subsystem 212. I/Osubsystem 212 is communicatively coupled to external I/O devices 214that may include, for example, data input devices, sensors and/or outputdevices, such as displays.

Another embodiment of a computing environment to incorporate and use oneor more aspects of the configuration architectural mode facility isdescribed with reference to FIG. 3A. In this example, a computingenvironment 300 includes, for instance, a native central processing unit(CPU) 302, a memory 304, and one or more input/output devices and/orinterfaces 306 coupled to one another via, for example, one or morebuses 308 and/or other connections. As examples, computing environment300 may include a PowerPC processor or a Power Systems server offered byInternational Business Machines Corporation, Armonk, N.Y.; an HPSuperdome with Intel Itanium II processors offered by Hewlett PackardCo., Palo Alto, Calif.; and/or other machines based on architecturesoffered by International Business Machines Corporation, Hewlett Packard,Intel, Oracle, or others.

Native central processing unit 302 includes one or more native registers310, such as one or more general purpose registers and/or one or morespecial purpose registers used during processing within the environment,as well as a configuration architectural mode facility 311. Theseregisters include information that represents the state of theenvironment at any particular point in time.

Moreover, native central processing unit 302 executes instructions andcode that are stored in memory 304. In one particular example, thecentral processing unit executes emulator code 312 stored in memory 304.This code enables the computing environment configured in onearchitecture to emulate one or more other architectures. For instance,emulator code 312 allows machines based on architectures other than thez/Architecture, such as PowerPC processors, Power Systems servers, HPSuperdome servers or others, to emulate the z/Architecture (and/orESA/390) and to execute software and instructions developed based on thez/Architecture.

Further details relating to emulator code 312 are described withreference to FIG. 3B. Guest instructions 350 stored in memory 304comprise software instructions (e.g., correlating to machineinstructions) that were developed to be executed in an architectureother than that of native CPU 302. For example, guest instructions 350may have been designed to execute on a z/Architecture processor 202, butinstead, are being emulated on native CPU 302, which may be, forexample, an Intel Itanium II processor. In one example, emulator code312 includes an instruction fetching routine 352 to obtain one or moreguest instructions 350 from memory 304, and to optionally provide localbuffering for the instructions obtained. It also includes an instructiontranslation routine 354 to determine the type of guest instruction thathas been obtained and to translate the guest instruction into one ormore corresponding native instructions 356. This translation includes,for instance, identifying the function to be performed by the guestinstruction and choosing the native instruction(s) to perform thatfunction.

Further, emulator code 312 includes an emulation control routine 360 tocause the native instructions to be executed. Emulation control routine360 may cause native CPU 302 to execute a routine of native instructionsthat emulate one or more previously obtained guest instructions and, atthe conclusion of such execution, return control to the instructionfetch routine to emulate the obtaining of the next guest instruction ora group of guest instructions. Execution of the native instructions 356may include loading data into a register from memory 304; storing databack to memory from a register; or performing some type of arithmetic orlogic operation, as determined by the translation routine.

Each routine is, for instance, implemented in software, which is storedin memory and executed by native central processing unit 302. In otherexamples, one or more of the routines or operations are implemented infirmware, hardware, software or some combination thereof. The registersof the emulated processor may be emulated using registers 310 of thenative CPU or by using locations in memory 304. In embodiments, guestinstructions 350, native instructions 356 and emulator code 312 mayreside in the same memory or may be disbursed among different memorydevices.

The computing environments described above are only examples ofcomputing environments that can be used. Other environments, includingbut not limited to, other non-partitioned environments, otherpartitioned environments, and/or other emulated environments, may beused; embodiments are not limited to any one environment.

In accordance with one or more aspects, a configuration architecturalmode (CAM) facility is installed in one or more processors (e.g.,central processing units) of a computing environment to controlreconfiguration of the environment. For instance, when CAM is installedin a computing environment that supports a plurality of architecturalmodes, the computing environment is reconfigured such that use of one ormore aspects of at least one of the architectural modes is restricted.

One particular example of a configuration architectural mode facility isthe Configuration z/Architecture Architectural Mode (CZAM) facility.Installation of CZAM is indicated by, for instance, a facilityinstallation indicator, e.g., bit 138, set to, for instance, one. In oneparticular example, when bit 138 is set to one, the CZAM facility isinstalled, and when installed, a normal reset and a clear reset placesthe configuration into the z/Architecture architectural mode. Thus, thefacility bit, e.g., bit 2, indicating the z/Architecture architecturalmode is active is also set to one, in one example.

Based on installation of CZAM, a computing environment (e.g., a singleprocessor, a logical partition, a virtual guest, etc.) is re-configuredsuch that one or more aspects of a selected architecture, e.g., ESA/390,is no longer supported. Those aspects that are no longer supportedand/or processes affected by installation of CZAM are described below.

Although in the embodiments described herein, the plurality ofarchitectural modes include a legacy architecture (e.g., ESA/390) and anenhanced architecture (e.g., z/Architecture) and aspects of the legacyarchitecture, ESA/390, are no longer supported, other embodiments mayinclude other architectures. ESA/390 and z/Architecture are onlyexamples.

One process that is affected by installation of CZAM is a power-onprocess. To describe how this process is affected, initially, a power-onprocess for an environment that supports multiple architecturalconfigurations and does not include the CZAM facility is described withreference to FIGS. 4A-4B, and then a power-on process for an environmentthat is configured for multiple architectural configurations and doesinclude the CZAM facility is described with reference to FIGS. 6A-6B.Power-on for a system includes, for instance, starting the system andinitiating a boot sequence or other means of initiating operations inthe system. It may correspond to a physical power-on, a hardware reset,and/or a virtual power-on (e.g., in an emulated system, a virtualmachine or a guest environment).

Referring initially to FIG. 4A, based on a processor of the computingenvironment being powered on and an operator key, e.g., a load-normal ora load-clear key, being activated, the processor enters a load state andsets the computing environment to a particular architectural mode, e.g.,ESA/390 mode, STEP 400. For instance, an initial program load (IPL),such as a channel control word (CCW) initial program load (IPL), isperformed, STEP 402. Initial program loading provides a manual means forcausing a program to be read from a designated device and for initiatingexecution of that program. A CCW-type IPL is initiated manually bysetting the load-unit-address controls to a four digit number todesignate an input device and by subsequently activating the load-clearor load-normal key for a particular CPU.

Activating the load-clear key causes a clear reset to be performed onthe configuration; and activating the load-normal key causes an initialCPU reset to be performed on this CPU (the CPU on which the key wasactivated), a CPU reset to be propagated to all other CPUs in theconfiguration, and a subsystem reset to be performed on the remainder ofthe configuration. Activating the load-clear key or the load-normal keysets the architectural mode (e.g., ESA/390).

In the loading part of the operation, after the resets have beenperformed, this CPU then enters the load state. This CPU does notnecessarily enter the stopped state during the execution of the resetoperations. The load indicator is on while the CPU is in the load state.

Subsequently, a channel-program read operation is initiated from the I/Odevice designated by the load-unit-address controls. The effect ofexecuting the channel program is as if a format-0 CCW beginning atabsolute storage location 0 specified a read command with the modifierbits zeros, a data address of zero, a byte count of 24, thechain-command and SLI flags ones, and all other flags zeros.

When the IPL input/output operation is completed successfully, asubsystem identification word for the IPL device is stored in selectedabsolute storage locations (e.g., locations 184-187), zeros are storedin other selected absolute storage locations (e.g., locations 188-191),and a new program status word (PSW) is loaded from selected absolutestorage locations (e.g., locations 0-7), STEP 404. The program statusword controls operations of the computing environment.

If the PSW loading is successful and no machine malfunctions aredetected, this CPU leaves the load state, and the load indicator isturned off. If the rate control is set to the process position, the CPUenters the operating state, and operation of the computing environmentproceeds under control of the new program status word (PSW), STEP 406.The booted computing environment then runs, STEP 408, as furtherdescribed with reference to FIG. 4B.

Referring to FIG. 4B, the booted computing environment is initiated inESA/390 mode, STEP 420, and thus, operations are performed in ESA/390mode, STEP 422. At some point, a request may be made to change thearchitectural mode from ESA/390 to z/Architecture. In particular, aprogram sends an order code (e.g., a code designating Set Architecture)to the processor, which issues a Signal Processor (SIGP) instructionwith the order code to switch from ESA/390 mode to z/Architecture mode,STEP 424. For instance, a CPU signaling and response facility is usedthat includes the Signal Processor instruction (described below) and amechanism to interpret and act on server order codes, including one forSet Architecture. The facility provides for communications among CPUs,including transmitting, receiving, and decoding a set of assigned ordercodes; initiating the specified operation; and responding to a signalingCPU. By using Set Architecture, the architectural mode is set to thedesired configuration, e.g., z/Architecture. Further details of thisprocessing are described further below.

Thereafter, a determination is made as to whether the SIGP operation wasaccepted, INQUIRY 426. Based on the return code, a number of errorconditions can be diagnosed, including an “invalid parameter” indicationwhen a determination has been made that the CPU is already in thearchitectural mode specified by the code (i.e., that the setarchitecture represents a switch to current mode itself, or whether itis a switch from one mode to another mode). If the SIGP is accepted andthe set architecture represents a legal mode switch operation, then allthe processors of the computing environment that received the SIGPoperation transition into z/Architecture mode using, for instance, theSet Architecture processing described herein, STEP 428. However, if theSIGP operation is not legal, an error is indicated, STEP 430.

As described above, the power-on operation loads a program status word.One embodiment of a format of a program status word (PSW) is describedwith reference to FIG. 5. Referring to FIG. 5, in this example, theformat of the program status word is an ESA/390 format, except that bit31 is shown as EA, as indicated below.

In one embodiment, a program status word 500 includes the followingfields, as one example:

-   -   Per Mask (R) 502: Bit 1 controls whether the CPU is enabled for        interruptions associated with program event recording (PER).        When the bit is zero, no PER event can cause an interruption.        When the bit is one, interruptions are permitted, subject to the        PER event mask bits in control register 9;    -   DAT Mode (T) 504: Bit 5 controls whether implicit dynamic        address translation (DAT) of logical and instruction addresses        used to access storage takes place. When the bit is zero, DAT is        off, and logical and instruction addresses are treated as real        addresses. When the bit is one, DAT is on, and the dynamic        address translation mechanism is invoked.    -   I/O Mask (IO) 506: Bit 6 controls whether the CPU is enabled for        I/O interruptions. When the bit is zero, an I/O interruption        cannot occur. When the bit is one, I/O interruptions are subject        to the I/O interruption subclass mask bits in control        register 6. When an I/O interruption subclass mask bit is zero,        an I/O interruption for that I/O interruption subclass cannot        occur; when the I/O interruption subclass mask bit is one, an        I/O interruption for that I/O interruption subclass can occur;    -   External Mask (EX) 508: Bit 7 controls whether the CPU is        enabled for interruption by conditions included in the external        class. When the bit is zero, an external interruption cannot        occur. When the bit is one, an external interruption is subject        to the corresponding external subclass mask bits in control        register 0. When the subclass mask bit is zero, conditions        associated with the subclass cannot cause an interruption. When        the subclass mask bit is one, an interruption in that subclass        can occur.    -   PSW Key (Key) 510: Bits 9-11 form the access key for storage        references by the CPU. If the reference is subject to        key-controlled protection, the PSW key is matched with a storage        key when information is stored or when information is fetched        from a location that is protected against fetching. However, for        one of the operands of each of Move to Primary, Move to        Secondary, Move with Key, Move with Source Key, and Move with        Destination Key, and for either or both operands of Move with        Optional Specifications, an access key specified as an operand        is used instead of the PSW key.    -   Bit 12 512: This bit indicates the current architectural mode.        It is set to one for the ESA/390 PSW format. For the        z/Architecture PSW format, this bit is defined to be zero. When        in z/Architecture mode, a load PSW extended (LPSWE) instruction        is defined for loading a true z/Architecture PSW (which has a        different format than the format described herein, including        having an instruction address in bits 64-127). However, an        ESA/390 load PSW (LPSW) is still supported and can be used to        load an ESA/390 format PSW. When LPSW is executed and the        computing environment is in z/Architecture mode, the processor        expands the ESA/390 format PSW to the z/Architecture format,        including inverting bit 12. This is the reverse of collapsing        the z/Architecture PSW format that the operating system performs        to create the ESA/390 format PSW. That is, in computing        environments that support both ESA/390 and z/Architecture, when        a copy of a PSW is placed in storage, the operating system        collapses the full z/Architecture PSW to the size and format of        an ESA/390 PSW. Thus, other software with PSW format        dependencies can be unaware of the z/Architecture PSW.    -   Machine Check Mask (M) 514: Bit 13 controls whether the CPU is        enabled for interruption by machine check conditions. When the        bit is zero, a machine check interruption cannot occur. When the        bit is one, machine check interruptions due to system damage and        instruction processing damage are permitted, but interruptions        due to other machine check subclass conditions are subject to        the subclass mask bits in control register 14.    -   Wait State (W) 516: When bit 14 is one, the CPU is waiting; that        is, no instructions are processed by the CPU, but interruptions        may take place. When bit 14 is zero, instruction fetching and        execution occur in the normal manner. The wait indicator is one        when the bit is one.    -   Problem State (P) 518: When bit 15 is one, the CPU is in the        problem state. When bit 15 is zero, the CPU is in the supervisor        state. In the supervisor state, all instructions are valid. In        the problem state, only those instructions are valid that        provide meaningful information to the problem program and that        cannot affect system integrity; such instructions are called        unprivileged instructions. The instructions that are not valid        in the problem state are called privileged instructions. When a        CPU in the problem state attempts to execute a privileged        instruction, a privileged operation exception is recognized.        Another group of instructions, called semiprivileged        instructions, are executed by a CPU in the problem state only if        specific authority tests are met; otherwise, a privileged        operation exception or some other program exception is        recognized, depending on the particular requirement which is        violated.    -   Address Space Control (AS) 520: Bits 16 and 17, in conjunction        with PSW bit 5, control the translation mode.    -   Condition Code (CC) 522: Bits 18 and 19 are the two bits of the        condition code. The condition code is set to 0, 1, 2, or 3        depending on the result obtained in executing certain        instructions. Most arithmetic and logical operations, as well as        some other operations, set the condition code. The instruction        BRANCH ON CONDITION can specify any selection of the condition        code values as a criterion for branching.    -   Program Mask 524: Bits 20-23 are the four program mask bits.        Each bit is associated with a program exception, as follows:

Program Mask Bit Program Exception 20 Fixed point overflow 21 Decimaloverflow 22 HFP exponent underflow 23 HFP significance

-   -   When the mask bit is one, the exception results in an        interruption. When the mask bit is zero, no interruption occurs.        The setting of the HFP-exponent-under-flow-mask bit of the        HFP-significance-mask bit also determines the manner in which        the operation is completed when the corresponding exception        occurs.    -   Extended Addressing Mode (EA) 526: Bit 31 controls the size of        effective addresses and effective address generation in        conjunction with bit 32, the basic addressing mode bit. When bit        31 is zero, the addressing mode is controlled by bit 32. When        bits 31 and 32 are both one, 64-bit addressing is specified.    -   Basic Addressing Mode (BA) 528: Bits 31 and 32 control the size        of effective addresses and effective address generation. When        bits 31 and 32 are both zero, 24-bit addressing is specified.        When bit 31 is zero and bit 32 is one, 31-bit addressing is        specified. When bits 31 and 32 are both one, 64-bit addressing        is specified. Bit 31 one and bit 32 zero is an invalid        combination that causes a specification exception to be        recognized. The addressing mode does not control the size of PER        addresses or of addresses used to access DAT, ASN, dispatchable        unit control, linkage, entry, and trace tables or access lists        or the linkage stack. The control of the addressing mode by bits        31 and 32 of the PSW is summarized as follows:

PSW:31 PSW:32 Addressing Mode 0 0 24-bit 0 1 31-bit 1 1 64-bit

-   -   Instruction Address 530: Bits 33-63 of the PSW are the        instruction address. The address designates the location of the        leftmost byte of the next instruction to be executed, unless the        CPU is in the wait state (bit 14 of the PSW is one).

In accordance with an aspect, when a configuration architectural modefacility, such as the Configuration z/Architecture Architectural Mode(CZAM) facility, is installed and activated in the computingenvironment, the power-on process is changed. One embodiment of a CZAMpower-on process is described with reference to FIG. 6A.

Referring to FIG. 6A, based on a processor of the computing environmentbeing powered on, the computing environment is set to the particulararchitectural mode specified by the configuration architectural modefacility, e.g., the z/Architecture mode (also referred to as ESAME) whenCZAM is installed, STEP 600. For instance, an initial program load(IPL), such as a channel control word (CCW) initial program load (IPL),is performed, as described above, STEP 602, and when the IPLinput/output operation is completed successfully, a subsystemidentification word for the IPL device is stored in selected absolutestorage locations (e.g., locations 184-187), zeros are stored in otherselected absolute storage locations (e.g., locations 188-191), and inthis embodiment, a 16-byte new program status word (PSW) is created fromselected absolute storage locations (e.g., locations 0-7), STEP 604. Thenew 16-byte PSW is formed, e.g., from the contents of the selectedstorage doubleword (e.g., locations 0-7). Bit 12 of the doubleword is tobe one; otherwise, an error may be indicated. (The error may be aspecification exception which is recognized, a machine check, or yetanother error indication.) Bits 0-32 of the newly created PSW are set tobits 0-32 of the selected doubleword, except with bit 12 inverted. Bits33-96 of the newly created PSW are set to zeros. Bit positions 97-127 ofthe newly created PSW are initialized from bits 33-63 of the selecteddoubleword.

In one embodiment, the PSW fields which are to be loaded by theinstruction are not checked for validity before they are loaded. In oneembodiment, bit 12 of the PSW is checked for validity. In yet anotherembodiment, all fields are checked for validity. In another embodiment,any bits not checked prior to the loading of the PSW are checked forvalidity after the PSW has been initialized, and the processor mayindicate an error (e.g., by raising a specification exception which isrecognized, a machine check, or yet another error indication.)

The computing environment enters the operating state, and operation ofthe computing environment proceeds under control of the new programstatus word (PSW), STEP 606. The booted computing environment then runs,STEP 608, as further described with reference to FIG. 6B.

Referring to FIG. 6B, the booted computing environment is initiated inz/Architecture mode, STEP 620, and thus, operations are performed inz/Architecture mode, STEP 622. No mode switch is necessary, andprocessing continues directly with processing in the z/Architecturemode. Thus, in one embodiment, the following steps are not needed: ASignal Processor (SIGP) operation to switch from ESA/390 mode toz/Architecture mode; a determination as to whether the SIGP operation isan accepted operation; the transition to z/Architecture if it is anaccepted operation; or the error indication, if the SIGP operation isnot accepted.

All of the processors of the computing environment (i.e., theenvironment being configured, e.g., single processor, logical partition,VM guest) are in z/Architecture mode, without performing the aboveindicated steps. Thus, as described herein, in accordance with oneaspect, the ability to boot or power-on in ESA/390 mode is removed fromthe computing environment that is configured for both ESA/390 andz/Architecture. In particular, although a computing environment isconfigured to support multiple architectures, a capability is providedto restrict certain aspects of at least one of the configuredarchitectures, one of the aspects being the ability to power-on in thatarchitecture.

In one or more embodiments, the powering-on in z/Architecture modeprovides a mechanism to specify one of (1) a logical partition(guest-1), and (2) a logical partition and guest-2 are to be booted andreset in z/Architecture mode, without the need to boot in ESA/390 mode.This feature may be installed unconditionally or under the control of aconfiguration switch.

The boot sequence with respect to PSW initialization is modified. Forinstance, at the end of IPL, the IPL PSW at absolute locations 0-7 isloaded. As is currently done when the reset condition is ESA/390, bit 12is one, making a valid ESA/390 IPL PSW, and the program proceeds toexecute instructions in the ESA/390 architectural mode. With CZAMinstalled, the reset condition is z/Architecture, bit 12 is still one,making a valid ESA/390 IPL PSW, but bit 12 is inverted during theformation of the 16 byte z/Architecture current PSW, as defined above.

In addition to the power-on process, other processes, behaviors and/oroperations may also be changed or affected by installation of aconfiguration architectural mode facility. These affected processes,behaviors, and/or operations are specific to the ESA/390 andz/Architecture modes. However, similar and/or different processes may beaffected for other types of architectures. Example processes, behaviorsand/or operations that may be affected in one or more embodimentsinclude, for instance:

(1) Enabling a switch from mode to self (e.g., from z/Architecture modeto z/Architecture mode) without generating an error (or ignoring theerror). That is, a processor may issue a SIGP instruction to switch toz/Architecture mode and if it is already in that mode, no error will begenerated. Previously, attempting a switch to the mode corresponding tothe current mode generated an error.

(2) Disabling a switch to ESA/390 mode. Based on installing andactivating CZAM, the switch to ESA/390 is disabled and now generates anerror. A switch back to ESA/390 is prevented by checking bit 12 of thePSW, and taking an exception, if bit 12 is not set to indicatez/Architecture mode (represented by a bit 12 of “1” in storage which isinverted to bit “0” to represent z/Architecture in the PSW when anESA/390 PSW is converted to a valid z/Architecture PSW).

(3) Modifying the Load PSW operation to restrict handling of bit 12. Ifthe Configuration z/Architecture Architectural Mode facility isinstalled, Load PSW recognizes a specification exception if bit 12 ofits second operand is not one. Load PSW loads bits 0-32 of its secondoperand, except with bit 12 inverted, and bits 33-63 of the operand asbits 0-32 and 97-127, respectively of the current PSW, and it sets bits33-96 of the current PSW to zeros.

Further details regarding the Load PSW instruction are described withreference to FIG. 7. In one embodiment, a Load PSW instruction 700includes an operation code field 702 that includes an operation code toindicate a load PSW operation; a base field (B₂) 704; and a displacementfield (D₂) 706. Contents of the general register designated by the B₂field are added to the contents of the D₂ field to form an address of asecond operand in storage (referred to as the second operand address).

In operation of the Load PSW instruction, the current PSW is replaced bya 16-byte PSW formed from the contents of the doubleword at the locationdesignated by the second operand address.

Bit 12 of the doubleword is to be one; otherwise, a specificationexception may be recognized, depending on the model. If theConfiguration z/Architecture Architectural Mode facility is installed,then a specification exception is recognized if bit 12 of the doublewordis not one.

Bits 0-32 of the doubleword, except with bit 12 inverted, are placed inpositions 0-32 of the current PSW. Bits 33-63 of the doubleword areplaced in positions 97-127 of the current PSW. Bits 33-96 of the currentPSW are set to zero.

A serialization and checkpoint synchronization function is performedbefore or after the operand is fetched and again after the operation iscompleted.

The operand is to be designated on a doubleword boundary; otherwise, aspecification exception is recognized. A specification exception may berecognized if bit 12 of the operand is zero, depending on the model.

The PSW fields which are to be loaded by the instruction are not checkedfor validity before they are loaded, except for the checking of bit 12.However, immediately after loading, a specification exception isrecognized, and a program interruption occurs, when any of the followingis true for the newly loaded PSW:

-   -   Any of bits 0, 2-4, 12, or 24-30 is a one.    -   Bits 31 and 32 are both zero, and bits 97-103 are not all zeros.    -   Bits 31 and 32 are one and zero, respectively.

In these cases, the operation is completed, and the resultinginstruction length code is 0.

The operation is suppressed on all addressing and protection exceptions.

Resulting Condition Code: The code is set as specified in the new PSWLoaded.

Program Exceptions:

-   -   Access (fetch, operand 2)    -   Privileged operation    -   Specification

Programming Note: The second operand should have the format of anESA/390 PSW. A specification exception will be recognized during orafter the execution of LOAD PSW if bit 12 of the operand is zero.

Further details regarding the PSW are described in “Development andAttributes of z/Architecture,” Plambeck et al., IBM J. Res. & Dev., Vol.46, No. 4/5, July/September 2002, which is hereby incorporated byreference herein in its entirety.

In addition to the above processes, operations and/or behaviors that maybe changed due to installation of a configuration architectural modefacility, the reset mode may also be changed in one or more embodiments,as explained below.

(4) Changes the reset mode (e.g., for reset, clear reset, and otheractions for reset). When the CZAM facility is installed, the CPU resetsets the architectural mode to the z/Architecture mode, if it is causedby activation of, for instance, the load-normal key.

There are a number of reset functions that are included as part of theESA/390 and z/Architecture modes, including, for instance, CPU reset,initial CPU reset, Subsystem reset, Clear reset and Power-on reset, eachof which is described below.

CPU Reset

CPU reset provides a means of clearing equipment check indications andany resultant unpredictability in the CPU state with the least amount ofinformation destroyed. In particular, it is used to clear checkconditions when the CPU state is to be preserved for analysis orresumption of the operation. If the Configuration z/ArchitectureArchitectural Mode (CZAM) facility is not installed, CPU reset sets thearchitectural mode to the ESA/390 mode if it is caused by activation ofthe load-normal key (an operator facility). When the CZAM facility isinstalled, CPU reset sets the architectural mode to the z/Architecturemode if it is caused by activation of the load-normal key. When CPUreset sets the ESA/390 mode, it saves the current PSW so that PSW can berestored by a Signal Processor Set Architecture order that changes thearchitectural mode back to z/Architecture.

CPU reset causes the following actions, in one embodiment:

-   -   1. The execution of the current instruction or other processing        sequence, such as an interruption, is terminated, and all        program-interruption and supervisor-call-interruption conditions        are cleared.    -   2. Any pending external-interruption conditions which are local        to the CPU are cleared. Floating external-interruption        conditions are not cleared.    -   3. Any pending machine-check-interruption conditions and error        indications which are local to the CPU and any check-stop states        are cleared. Floating machine-check-interruption conditions are        not cleared. Any machine-check condition which is reported to        all CPUs in the configuration and which has been made pending to        a CPU is said to be local to the CPU.    -   4. All copies of prefetched instructions or operands are        cleared. Additionally, any results to be stored because of the        execution of instructions in the current checkpoint interval are        cleared.    -   5. The ART (Access Register Translation)-lookaside buffer and        translation-lookaside buffer are cleared of entries.    -   6. If the reset is caused by activation of the load-normal key        on any CPU in the configuration, the following actions occur:        -   a. When the CZAM facility is not installed, the            architectural mode of the CPU (and of all other CPUs in the            configuration because of the initial CPU reset or CPU resets            performed by them) is changed from the z/Architecture mode            to the ESA/390 mode. If the CZAM facility is installed, the            architectural mode of the CPU (and of all other CPUs in the            configuration because of the initial CPU reset or CPU resets            performed by them) is set to the z/Architecture mode.        -   b. When the CZAM facility is not installed, the current PSW            is saved for subsequent use by a Signal Processor Set            Architecture order that restores the z/Architecture mode.        -   c. When the CZAM facility is not installed, the current PSW            is changed from 16 bytes to eight bytes. The bits of the            eight-byte PSW are set as follows: bits 0-11 and 13-32 are            set equal to the same bits of the 16-byte PSW, bit 12 is set            to one, and bits 33-63 are set equal to bits 97-127 of the            16-byte PSW.    -   A CPU reset caused by activation of the system reset-normal key        or by the Signal Processor CPU-Reset order, and any CPU reset in        the ESA/390 mode, do not affect the captured z/Architecture-PSW        register (i.e., a PSW saved when the CPU last went from the        z/Architecture mode to the ESA/390 mode because of a Set        Architecture order with code 0 or a CPU reset due to activation        of the load-normal key).    -   7. The CPU is placed in the stopped state after actions 1-6 have        been completed. When the CCW-type IPL sequence follows the reset        function on that CPU, the CPU enters the load state at the        completion of the reset function and does not necessarily enter        the stopped state during the execution of the reset operation.        When the list-directed IPL sequence follows the reset function        on that CPU, the CPU enters the operating state and does not        necessarily enter the stopped state during the execution of the        reset operation.

Registers, storage contents, and the state of conditions external to theCPU remain unchanged by CPU reset. However, the subsequent contents ofthe register, location, or state are unpredictable if an operation is inprogress that changes the contents at the time of the reset. A lock heldby the CPU when executing PERFORM LOCKED OPERATION is not released byCPU reset.

When the reset function in the CPU is initiated at the time the CPU isexecuting an I/O instruction or is performing an I/O interruption, thecurrent operation between the CPU and the channel subsystem may or maynot be completed, and the resultant state of the associatedchannel-subsystem facility may be unpredictable.

Programming Notes:

-   -   1. Most operations which would change a state, a condition, or        the contents of a field cannot occur when the CPU is in the        stopped state. However, some signal-processor functions and some        operator functions may change these fields. To eliminate the        possibility of losing a field when CPU reset is issued, the CPU        should be stopped, and no operator functions should be in        progress.    -   2. If the architectural mode is changed to the ESA/390 mode and        bit 31 of the current PSW is one, the PSW is invalid.

Initial CPU Reset

Initial CPU reset provides the functions of CPU reset together withinitialization of the current PSW, captured z/Architecture PSW, CPUtimer, clock comparator, prefix, breaking-event-address control,floating point control, and time-of-day (TOD) programmable registers. Ifthe CZAM facility is not installed, initial CPU reset sets thearchitectural mode to the ESA/390 mode if it is caused by activation ofthe load-normal key. When the CZAM facility is installed, initial CPUreset sets the architectural mode to the z/Architecture mode if it iscaused by activation of the load-normal key.

Initial CPU reset combines the CPU reset functions with the followingclearing and initializing functions:

-   -   1. When the CZAM facility is not installed, if the reset is        caused by activation of the load-normal key, the architectural        mode of the CPU (and of all other CPUs in the configuration) is        set to the ESA/390 mode. Otherwise, if the CZAM facility is        installed, the architectural mode of the CPU (and of all other        CPUs in the configuration) is set to the z/Architecture mode.    -   2. The contents of the current PSW, captured z/Architecture-PSW,        prefix, CPU timer, clock comparator, and TOD programmable        register are set to zero. When the IPL sequence follows the        reset function on that CPU, the contents of the PSW are not        necessarily set to zero.    -   3. The contents of the control registers are set to their        initial z/Architecture values. All 64 bits of the control        registers are set regardless of whether the CPU is in the        ESA/390 or the z/Architecture architectural mode.    -   4. The contents of the floating point control register are set        to zero.    -   5. The contents of the breaking-event-address register are        initialized to 0000000000000001 hex.

These clearing and initializing functions include validation.

Setting the current PSW to zero when the CPU is in the ESA/390architectural mode at the end of the operation causes the PSW to beinvalid, since PSW bit 12 is to be one in that mode. Thus, in this caseif the CPU is placed in the operating state after a reset without firstintroducing a new PSW, a specification exception is recognized.

Subsystem Reset

Subsystem reset provides a means for clearing floating interruptionconditions as well as for invoking I/O system reset.

Clear Reset

Clear reset causes initial CPU reset and subsystem reset to be performedand, additionally, clears or initializes all storage locations andregisters in all CPUs in the configuration, with the exception of theTOD clock. Such clearing is useful in debugging programs and in ensuringuser privacy. Clear reset also releases all locks used by the PERFORMLOCKED OPERATION instruction. If the CZAM facility is not installed,clear reset sets the architectural mode to the ESA/390 mode. When theCZAM facility is installed, clear reset sets the architectural mode tothe z/Architecture mode. Clearing does not affect external storage, suchas direct access storage devices used by the control program to hold thecontents of unaddressable pages.

Clear reset combines the initial CPU reset function with an initializingfunction which causes the following actions:

-   -   1. When the CZAM facility is not installed, the architectural        mode of all CPUs in the configuration is set to the ESA/390        mode. If the CZAM facility is installed, the architectural mode        of all CPUs in the configuration is set to the z/Architecture        mode.    -   2. The access, general, and floating point registers of all CPUs        in the configuration are set to zero. All 64 bits of the general        registers are set to zero regardless of whether the CPU was in        the ESA/390 or z/Architecture architectural mode when the        clear-reset function was initiated.    -   3. The contents of the main storage in the configuration and the        associated storage keys are set to zero with valid        checking-block code.    -   4. The locks used by any CPU in the configuration when executing        the PERFORM LOCKED OPERATION instruction are released.    -   5. A subsystem reset is performed.

Validation is included in setting registers and in clearing storage andstorage keys.

Programming Notes:

-   -   1. The architectural mode is not changed by activation of the        system-reset-normal key or by execution of a Signal Processor        CPU-Reset or Initial-CPU-reset order. All CPUs in the        configuration are in the same architectural mode.    -   2. For the CPU-reset operation not to affect the contents of        fields that are to be left unchanged, the CPU is not to be        executing instructions and is to be disabled for all        interruptions at the time of the reset. Except for the operation        of the CPU timer and for the possibility of a machine-check        interruption occurring, all CPU activity can be stopped by        placing the CPU in the wait state and by disabling it for I/O        and external interruptions. To avoid the possibility of causing        a reset at the time that the CPU timer is being updated or a        machine-check interruption occurs, the CPU is to be in the        stopped state.    -   3. CPU reset, initial CPU reset, subsystem reset, and clear        reset do not affect the value and state of the TOD clock.    -   4. The conditions under which the CPU enters the check-stop        state are model-dependent and include malfunctions that preclude        the completion of the current operation. Hence, if CPU reset or        initial CPU reset is executed while the CPU is in the check-stop        state, the contents of the PSW, registers, and storage        locations, including the storage keys and the storage location        accessed at the time of the error, may have unpredictable        values, and, in some cases, the contents may still be in error        after the check-stop state is cleared by these resets. In this        situation, a clear reset is required to clear the error.

Power-On Reset

The power-on reset function for a component of the machine is performedas part of the power-on sequence for that component. The power-onsequences for the TOD clock, main storage, expanded storage, and channelsubsystem may be included as part of the CPU power-on sequence, or thepower-on sequence for these units may be initiated separately.

CPU Power-On Reset: The power-on reset causes initial CPU reset to beperformed and may or may not cause I/O-system reset to be performed inthe channel subsystem. The contents of general registers, accessregisters, and floating-point registers are cleared to zeros with validchecking-block code. Locks used by PERFORM LOCKED OPERATION andassociated with the CPU are released unless they are held by a CPUalready powered on. If the CZAM facility is not installed and the resetis associated with establishing a configuration, the CPU is placed inthe ESA/390 mode; otherwise, the CPU is placed in the architectural modeof the CPUs already in the configuration. If the CZAM facility isinstalled, the CPU is placed in the z/Architecture mode.

CPU reset, initial CPU reset, subsystem reset, and clear reset may beinitiated manually by using the operator facilities. Initial CPU resetis part of the initial program loading function. Power-on reset isperformed as part of turning power on.

When the CZAM facility is not installed, if the reset is initiated bythe system-reset-clear, load-normal, or load-clear key or by a CPUpower-on reset that establishes the configuration, the architecturalmode is set to the ESA/390 mode; otherwise, the architectural mode isunchanged, except that power-on reset sets the mode to that of the CPUsalready in the configuration. If the CZAM facility is installed, thearchitectural mode is set to the z/Architecture mode.

Other processes, operations and/or behaviors that may be changed due toinstallation of a configuration architectural mode facility aredescribed below:

(5) Suppresses other reset related actions that are taken to facilitatechange between ESA/390 and z/Architecture mode, when reset is performed.When the CZAM facility is not installed, the current PSW is saved forsubsequent use by a Signal Processor Set Architecture order thatrestores the z/Architecture mode. When the CZAM facility is notinstalled, the current PSW is changed from 16 bytes to eight bytes. Thebits of the eight byte PSW are set as follows, in one example: bits 0-11and 13-32 are set equal to the same bits of the 16-byte PSW, bit 12 isset to one, and bits 33-63 are set equal to bits 97-127 of the 16 bytePSW. When the CZAM facility is installed, the PSW is not saved forsubsequent used by a Signal Processor Set Architecture order thatrestores the z/Architecture mode, and the current PSW is not changedfrom 16 bytes to 8 bytes.

(6) Changes the process for configuring a CPU with a configure CPU SCLP(Service Call Logical Processor) command, and load key operations.Rather than configuring in ESA/390, configure in the mode defined byreset. The configure CPU SCLP command places the subject CPU in thearchitectural mode of the CPUs already in the configured state. At leastthe first CPU placed in a configuration is placed there in conjunctionwith a CPU power on reset and, as part of that reset, is placed in thearchitecture mode defined in CPU power on reset. A model mayalternatively set the mode of CPUs that are in the standby state when itsets the mode of the configured CPUs.

Activating the load-clear key or the load-normal key sets thearchitectural mode as defined in clear reset or initial CPU reset,respectively.

(7) Changes SIGP so as not to allow a Set Architecture order to changethe architectural mode to ESA/390.

One embodiment of a Signal Processor (SIGP) instruction is describedwith reference to FIG. 8A. In one embodiment, a Signal Processorinstruction 800 has a plurality of fields, including, for instance, anoperation code field (opcode) 802 having an operation code indicating asignal processor operation; a first register field (R₁) 804; a secondregister field (R₃) 806; a base field (B₂) 808; and a displacement field(D₂) 810. R₁ designates a general register, the contents of which arethe first operand; R₃ designates a general register, the contents ofwhich are the third operand; and the contents of a register designatedby R₂ are added to the displacement in D₂ to provide an address of asecond operand.

In operation, an eight-bit order code and, if called for, a 32-bitparameter are transmitted to the CPU designated by the CPU addresscontained in the third operand. The result is indicated by the conditioncode and may be detailed by status assembled in bit positions 32-63 ofthe first-operand location.

The second-operand address is not used to address data; instead, bits56-63 of the address contain the eight-bit order code. Bits 0-55 of thesecond-operand address are ignored. The order code specifies thefunction to be performed by the addressed CPU. The assignment anddefinition of order codes include, for instance, the following, in oneexample:

Code (Dec) (Hex) Order 0 00 Unassigned 1 01 Sense 2 02 External call 303 Emergency signal 4 04 Start 5 05 Stop 6 06 Restart 7 07 Unassigned 808 Unassigned 9 09 Stop and store status 10  0A Unassigned 11  0BInitial CPU reset 12  0C CPU reset 13  0D Set prefix 14  0E Store statusat address 15-17 0F-11 Unassigned 18  12 Set architecture 19  13Conditional Emergency Signal 14  14 Unassigned 21  15 Sense RunningStatus  22-255 16-FF Unassigned

The 16-bit binary number contained in bit positions 48-63 of generalregister R₃ forms the CPU address. Bits 0-47 of the register areignored. When the specified order is the Set Architecture order, the CPUaddress is ignored; all other CPUs in the configuration are consideredto be addressed.

The general register containing the 32-bit parameter in bit positions32-63 is R₁ or R₁+1, whichever is the odd-numbered register. It dependson the order code whether a parameter is provided and for what purposeit is used.

-   -   The operands just described have the following formats, in one        example:    -   General register designated by Bits 0-31 unused; bits 32-63        include status;    -   General register designated by R₁ or R₁+1, which ever is the        odd-numbered register: Bits 0-31 unused; bits 32-63 include the        parameter;    -   General register designated by R₃: Bits 0-48 unused; bits 49-63        include the CPU address;    -   Second-operand address: Bits 0-55 unused; bits 56-63 include the        order code.

A serialization function is performed before the operation begins andagain after the operation is completed.

When the order code is accepted and no nonzero status is returned,condition code 0 is set. When status information is generated by thisCPU (the CPU performing the SIGP) or returned by the addressed CPU, thestatus is placed in bit positions 32-63 of general register R₁, bits0-31 of the register remain unchanged, and condition code 1 is set.

When the access path to the addressed CPU is busy, or the addressed CPUis operational but in a state where it cannot respond to the order code,condition code 2 is set.

When the addressed CPU is not operational (that is, it is not providedin the installation, it is not in the configuration, it is in any ofcertain customer-engineer test modes, or its power is off), conditioncode 3 is set.

Resulting Condition Code:

0 Order code accepted 1 Status stored 2 Busy 3 Not operational

Program Exceptions:

-   -   Privileged operation    -   Transactional constraint

When the Set Architecture Signal Processor order is specified in bitpositions 56-63 of the second operand address of the Signal Processorinstruction, the contents of bit positions 56-63 of the parameterregister are used as a code specifying an architectural mode to whichall CPUs in the configuration are to be set: code 0 specifies theESA/390 mode, and codes 1 and 2 specify the z/Architecture mode. Code 1specifies that, for each of all CPUs in the configuration, the currentESA/390 PSW is to be transformed to a z/Architecture PSW. Code 2specifies that the PSW of the CPU executing Signal Processor is to betransformed to a z/Architecture PSW and that, for each of all other CPUsin the configuration, the PSW is to be set with the value of thecaptured z/Architecture-PSW register for that CPU. The setting of thePSW with the value of the captured-z/Architecture-PSW register willrestore the PSW that existed when the CPU was last in the z/Architecturemode, provided that the captured-z/Architecture-PSW register has notbeen set to all zeros by a reset.

Bits 0-55 of the parameter register are ignored. The contents of theCPU-address register of the Signal Processor instruction are ignored;all other CPUs in the configuration are considered to be addressed.

When the CZAM facility is not installed, the order is accepted only ifthe code is 0, 1, or 2, the CPU is not already in the mode specified bythe code, each of all other CPUs is in either the stopped or thecheck-stop state, and no other condition precludes accepting the order.

When the CZAM facility is installed, code 0 is not accepted because areturn to the ESA/390 mode is not permitted, and since the CPU isalready in the z/Architecture architectural mode, specification of codes1 and 2 result in a completion indicating invalid-parameter andcondition code 1. The other prerequisite conditions normally verified bythe Set Architecture order may or may not be checked.

If accepted, the order is completed by all CPUs during the execution ofSignal Processor. In no case, in this embodiment, can different CPUs bein different architectural modes.

The Set Architecture order is completed, as follows, in one example:

-   -   If the code in the parameter register is not 0, 1, or 2, or if        the CPU is already in the architectural mode specified by the        code, the order is not accepted. Instead, bit 55 (invalid        parameter) of the general register designated by the R₁ field of        the Signal Processor instruction is set to one, and condition        code 1 is set.    -   If it is not true that all other CPUs in the configuration are        in the stopped or check-stop state, the order is not accepted.        Instead, bit 54 (incorrect state) of the general register        designated by the R₁ field of the Signal Processor instruction        is set to one, and condition code 1 is set.    -   The architectural mode of all CPUs in the configuration is set        as specified by the code (e.g., bit 12 of the PSW to control        operations is set to the specified architectural mode, and/or        another indication in the computing environment is set        indicating the specified architectural mode).    -   If the order changes the architectural mode from ESA/390 to        z/Architecture and the code is 1, then, for each CPU in the        configuration, the eight-byte current PSW is changed to a        16-byte PSW, and the bits of the 16-byte PSW are set as follows:        bits 0-11 and 13-32 are set equal to the same bits of the        eight-byte PSW, bit 12 and bits 33-96 are set to zeros, and bits        97-127 are set equal to bits 33-63 of the eight-byte PSW. Also,        bit 19 of the ESA/390 prefix, which becomes bit 51 of the        z/Architecture prefix, is set to zero.

If the code is 2, the PSW of the CPU executing Signal Processor and theprefix values of all CPUs are set as in the code-1 case. For each of allother CPUs in the configuration, the PSW is set with the value of thecaptured-z/Architecture-PSW register. However, thecaptured-z/Architecture-PSW register has been set to all zeros if theCPU performed a reset, other than CPU reset, either at the time of thearchitectural-mode transition or subsequently.

-   -   If the order changes the architectural mode from z/Architecture        to ESA/390, then, for each CPU in the configuration, (1) the        current PSW, which is the updated PSW in the case of the CPU        executing Signal Processor, is saved in the        captured-z/Architecture-PSW register, and (2) the 16-byte        current PSW is changed to an eight-byte PSW by setting the bits        of the eight-byte PSW as follows: bits 0-11 and 13-32 are set        equal to the same bits of the 16-byte PSW, bit 12 is set to one,        and bits 33-63 are set equal to bits 97-127 of the 16-byte PSW.        Bit 51 of the z/Architecture prefix, which becomes bit 19 of the        ESA/390 prefix, remains unchanged.    -   The ALBs and TLBs of all CPUs in the configuration are cleared        of their contents.    -   A serialization and checkpoint-synchronization function is        performed on all CPUs in the configuration.

If the order changes the architectural mode from z/Architecture toESA/390 and the Signal Processor instruction causes occurrence of aninstruction-fetching PER event, only the rightmost 31 bits of theaddress of the instruction are stored in the ESA/390 PER-address field.

In one embodiment, with CZAM, the following is a prerequisite: Each ofall other CPUs is in either the stopped or the check-stop state, and noother condition precludes accepting the order. When the CZAM facility isinstalled, code 0 is not accepted because a return to the ESA/390 modeis not permitted, and since the CPU is already in the z/Architecturalarchitectural mode, specification of codes 1 and 2 result in acompletion indicating invalid parameter and condition code 1. The otherprerequisite conditions normally verified by the Set Architecture ordermay or may not be checked. In yet another embodiment, SIGP with code 1and 2 indicates successful completion without further indication.

One embodiment of processing associated with executing a SIGPinstruction for a Set Architecture order code is described withreference to FIG. 8B. Referring to FIG. 8B, a processor of the computingenvironment executes a SIGP instruction and obtains an order code thatindicates a Set Architecture operation, STEP 850. In one example, theorder code is included in the second-operand address of the SIGPinstruction.

Additionally, the requested architectural mode to be switched to isobtained from, e.g., the parameter register specified by the SIGPinstruction, STEP 852. Further, a determination is made as to whether aconfiguration architectural mode facility, such as CZAM, is installed,INQUIRY 854. This is determined, in one example, by a facilityindicator.

If CZAM is not installed, then a further determination is made as towhether the CPU is already in the requested architectural mode, INQUIRY856. If so, then status is provided in, e.g., a register designated bythe SIGP instruction, STEP 858, and the status is treated as an error,STEP 860. However, if the CPU is not in the requested mode, INQUIRY 856,then a determination is made as to whether other conditions specified bythe instruction, such as whether the other CPUs of the computingenvironment being configured are in a stopped state, etc., are met,INQUIRY 862. If the conditions are not met, then processing continues toSTEP 858. Otherwise, the order is accepted, STEP 864, and thearchitectural mode is to be changed. Thus, the PSW is set, as describedabove, STEP 866, and processing for this aspect of the instruction ends,STEP 868.

Returning to INQUIRY 854, if CZAM is installed, then a determination ismade as to whether the CPU is in the requested mode, INQUIRY 870. If theCPU is already in the requested mode, then, in one example, status isprovided that the CPU is already in the requested architectural mode(e.g., z/Architecture), STEP 872. In this embodiment, however, thisstatus is acceptable and not treated as an error, STEP 874. Either, itis ignored, or in another embodiment, a condition code may be providedthat is a non-error code. In yet a further embodiment, the status merelyindicates successful completion. Other possibilities also exist toindicate no error even though the CPU is already in the requestedarchitectural mode.

Returning to INQUIRY 870, if however, the CPU is not in the requestedmode, then the order is not accepted, since it is illegal to return tothe one architectural mode (e.g., ESA/390), STEP 876. Status isprovided, STEP 878, which is considered an error, STEP 880.

In one embodiment, when CZAM is in a system as a non-selectablefacility, then INQUIRY 854 may be omitted and control may pass from STEP852 directly to STEP 870. In such an embodiment, STEPs 854 to 868 maynot be implemented.

In another embodiment, when an order to switch to the currentarchitecture mode is received, the order may not be accepted and anerror may be indicated in STEP 874.

Other behaviors, processes and/or operations that may change based oninstallation of a CAM include:

(8) Changes to the facility bits: A new bit, e.g., bit 138, is added tothe facility bits to indicate the Configuration z/ArchitectureArchitectural Mode facility, and bit 2, which indicates whether thez/Architectural architectural mode is active, is to be set to one(indicating active).

In at least one embodiment, the CZAM facility is installed for LPARs andguest-1 (first level guests—guests initiated by a hypervisor (e.g., byissuing a Start Interpretive Execution (SIE) instruction), but not forguest-2 (second level guests—a guest started by another guest (e.g., byissuing a SIE instruction).

In at least one embodiment, when CZAM is installed and a z/Architectureguest-2 is initiated, the guest is initiated in z/Architecture mode inaccordance with the technique of FIG. 6A. However, when CZAM isinstalled, and an ESA/390 guest-2 is initiated, it is initiated inESA/390 mode, in accordance with the technique of FIG. 4A, since it isnot affected by CZAM, in this embodiment. Thus, the host and first levelguests are controlled by CZAM, in which they will be initiated/reset,etc. in z/Architecture, regardless of preference for architectural mode(e.g., forced to be in z/Architecture, since ESA/390 not supported), butthe second level ESA/390 guests are not affected by CZAM and willcontinue to be initiated/reset, etc. in ESA/390.

As described herein, based on installing a configuration architecturalmode facility, such as a Configuration z/Architecture Architectural Modefacility, certain processes, operations and/or behaviors of a computingenvironment that is configured for multiple architectural modes arechanged. One such process is the power-on process. Further aspects ofprocessing associated with a power-on process when a configurationarchitectural mode facility is installed are described with reference toFIG. 9.

Referring to FIG. 9, initially a determination is made as to whether aconfiguration architectural mode facility is installed in a computingenvironment configured for a plurality of architectural modes and has adefined power-on sequence to power-on the computing environment in onearchitectural mode (e.g., a legacy mode, such as ESA/390), STEP 900. Theone architectural mode including a first instruction set architectureand having a first set of supported features, such as 31-bit addressing,use of 32-bit general purpose registers, and various features. If it isdetermined that the configuration architectural mode facility is notinstalled, INQUIRY 902, then the current power-on sequence is performed,STEP 904, as described with reference to FIGS. 4A-4B. Otherwise, thecomputing environment is reconfigured to restrict use of the onearchitectural mode (e.g., the legacy ESA/390 mode), STEP 906. Thereconfiguration includes, for instance, selecting a different power-onsequence to power-on the computing environment in another architecturalmode (e.g., a later or enhanced version of the architecture mode—e.g.,z/Architecture), STEP 908. The another architectural mode including asecond instruction set architecture and having a second set of supportedfeatures, such as 64-bit addressing, use of 64-bit general purposeregisters and various facilities, such as dynamic address translation,and/or other facilities. The power-on sequence is then executed topower-on the computing environment in the other architectural moderestricting use of the one architectural mode, STEP 910, as described,for instance, with reference to FIGS. 6A-6B. In one example, thisexecuting includes loading the PSW and inverting bit 12. Thereafter, thecomputing environment is run in the other architectural mode (e.g.,z/Architecture), STEP 912.

In a further embodiment, referring to FIG. 10, the reconfiguringincludes disabling one or more operations that support the onearchitectural mode, including disabling the switch operation, STEP 1000.For instance, the Signal Processor instruction is altered to provide anerror based on a request to switch back to the one architectural mode,e.g., ESA/390.

Further, one or more other processes, operations and/or behaviors arechanged to support power-on in the other architectural mode, instead ofthe one architectural mode and use of the one architectural mode isrestricted, STEP 1002. These one or more other processes include, forinstance, the configure CPU SCLP command that places the CPU in thearchitectural mode of the CPUs already in the configured state 1004; theload-clear key and load-normal key, which are operator facilities thatset the architecture mode as defined in clear reset or initial CPUreset, respectively 1006; the Signal Processor instruction that ischanged to accept a switch from an architectural mode to the samearchitectural mode, such that status is provided and not treated as anerror 1008; and facility bits are added to the facility indicators toindicate the configuration architectural mode facility 1010.

As described herein, another operation that is affected by installationof the configuration architectural mode facility is the reset operation.One embodiment of processing associated with reset is described withreference to FIG. 11. Initially, a processor obtains (e.g., receives, isprovided, or otherwise gets) a reset operation, STEP 1100, and the resetoperation is performed to reset the computing environment to the otherarchitectural mode (e.g., z/Architecture), STEP 1102, as describedherein. This includes, for instance, using a PSW that is in theappropriate format for the architecture and setting bit 12 in the PSW tozero.

Described in detail herein is a configuration architectural modefacility that restricts use of certain architectural aspects of anarchitecture supported by a computing environment configured for aplurality of architectures. In one example, a configurationarchitectural mode facility is installed, and a computing environmentthat supports multiple architectural configurations can be re-configuredsuch that aspects of one of the architectural modes (e.g., the legacymode) are no longer supported, but another architectural mode (e.g., anenhanced architectural mode) remains supported. When a computingenvironment is so configured, the computing environment is preventedfrom being reconfigured back to the unsupported architectural mode.

In a further embodiment, a computing environment is dynamicallyconfigured in a selected architectural mode, such as z/Architecture. Inthis embodiment, a check may not be made as to whether a CZAM facilityis installed, and/or an explicit SIGP Set Architecture order may not beperformed. One embodiment of the logic to perform this configuration isdescribed with reference to FIG. 12.

Referring to FIG. 12, in one embodiment, a processor configures acomputing environment to perform operations in a selected architecturalmode (e.g., z/Architecture), STEP 1200. The configuring includes, forinstance, commencing initialization of the computing environment using astored program status word, STEP 1202. In one example, the storedprogram status word has a format of an architectural mode different fromthe selected architectural mode. Thus, a determination is made that thestored program status word has the format of the architectural modedifferent from the selected architectural mode, STEP 1204. Based on thatdetermination, the stored program status word is automatically modifiedto have a format of the selected architectural mode, STEP 1206. Theautomatically modifying is performed absent an explicit request toswitch to the selected architectural mode. Initialization of thecomputing environment using the modified program status word is thencompleted to configure the computing environment in the selectedarchitectural mode, STEP 1208.

In one embodiment, the CZAM facility may be used with one or more otherfacilities including, for instance, a No-DAT facility and/or a controlutility boot facility, described in the following co-filed, commonlyassigned applications entitled “Managing Processing Associated withSelected Architectural Facilities,” Gainey, et al., (IBM Docket No.:POU920140020US1); and “Common Boot Sequence for Control Utility Able tobe Initialized in Multiple Architectures,” Michael K. Gschwind, (IBMDocket No.: POU920140019US1), respectively, each of which is herebyincorporated by reference herein in its entirety.

Referring to FIG. 13, in one example, a computer program product 1300includes, for instance, one or more non-transitory computer readablestorage media 1302 to store computer readable program code means, logicand/or instructions 1304 thereon to provide and facilitate one or moreembodiments.

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

In addition to the above, one or more aspects may be provided, offered,deployed, managed, serviced, etc. by a service provider who offersmanagement of customer environments. For instance, the service providercan create, maintain, support, etc. computer code and/or a computerinfrastructure that performs one or more aspects for one or morecustomers. In return, the service provider may receive payment from thecustomer under a subscription and/or fee agreement, as examples.Additionally or alternatively, the service provider may receive paymentfrom the sale of advertising content to one or more third parties.

In one aspect, an application may be deployed for performing one or moreembodiments. As one example, the deploying of an application comprisesproviding computer infrastructure operable to perform one or moreembodiments.

As a further aspect, a computing infrastructure may be deployedcomprising integrating computer readable code into a computing system,in which the code in combination with the computing system is capable ofperforming one or more embodiments.

As yet a further aspect, a process for integrating computinginfrastructure comprising integrating computer readable code into acomputer system may be provided. The computer system comprises acomputer readable medium, in which the computer medium comprises one ormore embodiments. The code in combination with the computer system iscapable of performing one or more embodiments.

Although various embodiments are described above, these are onlyexamples. For example, computing environments of other architectures canbe used to incorporate and use one or more embodiments. Further,different instructions, instruction formats, instruction fields and/orinstruction values may be used. Yet further, other types of processes,operations and/or behaviors may be affected by installation of a CAM.Many variations are possible.

Further, other types of computing environments can benefit and be used.As an example, a data processing system suitable for storing and/orexecuting program code is usable that includes at least two processorscoupled directly or indirectly to memory elements through a system bus.The memory elements include, for instance, local memory employed duringactual execution of the program code, bulk storage, and cache memorywhich provide temporary storage of at least some program code in orderto reduce the number of times code must be retrieved from bulk storageduring execution.

Input/Output or I/O devices (including, but not limited to, keyboards,displays, pointing devices, DASD, tape, CDs, DVDs, thumb drives andother memory media, etc.) can be coupled to the system either directlyor through intervening I/O controllers. Network adapters may also becoupled to the system to enable the data processing system to becomecoupled to other data processing systems or remote printers or storagedevices through intervening private or public networks. Modems, cablemodems, and Ethernet cards are just a few of the available types ofnetwork adapters.

Referring to FIG. 14, representative components of a Host Computersystem 5000 to implement one or more embodiments are portrayed. Therepresentative host computer 5000 comprises one or more CPUs 5001 incommunication with computer memory (i.e., central storage) 5002, as wellas I/O interfaces to storage media devices 5011 and networks 5010 forcommunicating with other computers or SANs and the like. The CPU 5001 iscompliant with an architecture having an architected instruction set andarchitected functionality. The CPU 5001 may have access registertranslation (ART) 5012, which includes an ART lookaside buffer (ALB)5013, for selecting an address space to be used by dynamic addresstranslation (DAT) 5003 for transforming program addresses (virtualaddresses) into real addresses of memory. A DAT typically includes atranslation lookaside buffer (TLB) 5007 for caching translations so thatlater accesses to the block of computer memory 5002 do not require thedelay of address translation. Typically, a cache 5009 is employedbetween computer memory 5002 and the processor 5001. The cache 5009 maybe hierarchical having a large cache available to more than one CPU andsmaller, faster (lower level) caches between the large cache and eachCPU. In some implementations, the lower level caches are split toprovide separate low level caches for instruction fetching and dataaccesses.

In one embodiment, an instruction is fetched from memory 5002 by aninstruction fetch unit 5004 via a cache 5009. The instruction is decodedin an instruction decode unit 5006 and dispatched (with otherinstructions in some embodiments) to instruction execution unit or units5008. Typically several execution units 5008 are employed, for examplean arithmetic execution unit, a floating point execution unit and abranch instruction execution unit. The instruction is executed by theexecution unit, accessing operands from instruction specified registersor memory as needed. If an operand is to be accessed (loaded or stored)from memory 5002, a load/store unit 5005 typically handles the accessunder control of the instruction being executed. Instructions may beexecuted in hardware circuits or in internal microcode (firmware) or bya combination of both.

As noted, a computer system includes information in local (or main)storage, as well as addressing, protection, and reference and changerecording. Some aspects of addressing include the format of addresses,the concept of address spaces, the various types of addresses, and themanner in which one type of address is translated to another type ofaddress. Some of main storage includes permanently assigned storagelocations. Main storage provides the system with directly addressablefast-access storage of data. Both data and programs are to be loadedinto main storage (from input devices) before they can be processed.

Main storage may include one or more smaller, faster-access bufferstorages, sometimes called caches. A cache is typically physicallyassociated with a CPU or an I/O processor. The effects, except onperformance, of the physical construction and use of distinct storagemedia are generally not observable by the program. Separate caches maybe maintained for instructions and for data operands. Information withina cache is maintained in contiguous bytes on an integral boundary calleda cache block or cache line (or line, for short). A model may provide anEXTRACT CACHE ATTRIBUTE instruction which returns the size of a cacheline in bytes. A model may also provide PREFETCH DATA and PREFETCH DATARELATIVE LONG instructions which effects the prefetching of storage intothe data or instruction cache or the releasing of data from the cache.

Storage is viewed as a long horizontal string of bits. For mostoperations, accesses to storage proceed in a left-to-right sequence. Thestring of bits is subdivided into units of eight bits. An eight-bit unitis called a byte, which is the basic building block of all informationformats. Each byte location in storage is identified by a uniquenonnegative integer, which is the address of that byte location or,simply, the byte address. Adjacent byte locations have consecutiveaddresses, starting with 0 on the left and proceeding in a left-to-rightsequence. Addresses are unsigned binary integers and are 24, 31, or 64bits.

Information is transmitted between storage and a CPU or a channelsubsystem one byte, or a group of bytes, at a time. Unless otherwisespecified, in, for instance, the z/Architecture, a group of bytes instorage is addressed by the leftmost byte of the group. The number ofbytes in the group is either implied or explicitly specified by theoperation to be performed. When used in a CPU operation, a group ofbytes is called a field. Within each group of bytes, in, for instance,the z/Architecture, bits are numbered in a left-to-right sequence. Inthe z/Architecture, the leftmost bits are sometimes referred to as the“high-order” bits and the rightmost bits as the “low-order” bits. Bitnumbers are not storage addresses, however. Only bytes can be addressed.To operate on individual bits of a byte in storage, the entire byte isaccessed. The bits in a byte are numbered 0 through 7, from left toright (in, e.g., the z/Architecture). The bits in an address may benumbered 8-31 or 40-63 for 24-bit addresses, or 1-31 or 33-63 for 31-bitaddresses; they are numbered 0-63 for 64-bit addresses. In one example,bits 8-31 and 1-31 apply to addresses that are in a location (e.g.,register) that is 32 bits wide, whereas bits 40-63 and 33-63 apply toaddresses that are in a 64-bit wide location. Within any otherfixed-length format of multiple bytes, the bits making up the format areconsecutively numbered starting from 0. For purposes of error detection,and in preferably for correction, one or more check bits may betransmitted with each byte or with a group of bytes. Such check bits aregenerated automatically by the machine and cannot be directly controlledby the program. Storage capacities are expressed in number of bytes.When the length of a storage-operand field is implied by the operationcode of an instruction, the field is said to have a fixed length, whichcan be one, two, four, eight, or sixteen bytes. Larger fields may beimplied for some instructions. When the length of a storage-operandfield is not implied but is stated explicitly, the field is said to havea variable length. Variable-length operands can vary in length byincrements of one byte (or with some instructions, in multiples of twobytes or other multiples). When information is placed in storage, thecontents of only those byte locations are replaced that are included inthe designated field, even though the width of the physical path tostorage may be greater than the length of the field being stored.

Certain units of information are to be on an integral boundary instorage. A boundary is called integral for a unit of information whenits storage address is a multiple of the length of the unit in bytes.Special names are given to fields of 2, 4, 8, 16, and 32 bytes on anintegral boundary. A halfword is a group of two consecutive bytes on atwo-byte boundary and is the basic building block of instructions. Aword is a group of four consecutive bytes on a four-byte boundary. Adoubleword is a group of eight consecutive bytes on an eight-byteboundary. A quadword is a group of 16 consecutive bytes on a 16-byteboundary. An octoword is a group of 32 consecutive bytes on a 32-byteboundary. When storage addresses designate halfwords, words,doublewords, quadwords, and octowords, the binary representation of theaddress contains one, two, three, four, or five rightmost zero bits,respectively. Instructions are to be on two-byte integral boundaries.The storage operands of most instructions do not have boundary-alignmentrequirements.

On devices that implement separate caches for instructions and dataoperands, a significant delay may be experienced if the program storesinto a cache line from which instructions are subsequently fetched,regardless of whether the store alters the instructions that aresubsequently fetched.

In one example, the embodiment may be practiced by software (sometimesreferred to licensed internal code, firmware, micro-code, milli-code,pico-code and the like, any of which would be consistent with one ormore embodiments). Referring to FIG. 14, software program code whichembodies one or more aspects may be accessed by processor 5001 of thehost system 5000 from long-term storage media devices 5011, such as aCD-ROM drive, tape drive or hard drive. The software program code may beembodied on any of a variety of known media for use with a dataprocessing system, such as a diskette, hard drive, or CD-ROM. The codemay be distributed on such media, or may be distributed to users fromcomputer memory 5002 or storage of one computer system over a network5010 to other computer systems for use by users of such other systems.

The software program code includes an operating system which controlsthe function and interaction of the various computer components and oneor more application programs. Program code is normally paged fromstorage media device 5011 to the relatively higher-speed computerstorage 5002 where it is available for processing by processor 5001. Thetechniques and methods for embodying software program code in memory, onphysical media, and/or distributing software code via networks are wellknown and will not be further discussed herein. Program code, whencreated and stored on a tangible medium (including but not limited toelectronic memory modules (RAM), flash memory, Compact Discs (CDs),DVDs, Magnetic Tape and the like is often referred to as a “computerprogram product”. The computer program product medium is typicallyreadable by a processing circuit preferably in a computer system forexecution by the processing circuit.

FIG. 15 illustrates a representative workstation or server hardwaresystem in which one or more embodiments may be practiced. The system5020 of FIG. 15 comprises a representative base computer system 5021,such as a personal computer, a workstation or a server, includingoptional peripheral devices. The base computer system 5021 includes oneor more processors 5026 and a bus employed to connect and enablecommunication between the processor(s) 5026 and the other components ofthe system 5021 in accordance with known techniques. The bus connectsthe processor 5026 to memory 5025 and long-term storage 5027 which caninclude a hard drive (including any of magnetic media, CD, DVD and FlashMemory for example) or a tape drive for example. The system 5021 mightalso include a user interface adapter, which connects the microprocessor5026 via the bus to one or more interface devices, such as a keyboard5024, a mouse 5023, a printer/scanner 5030 and/or other interfacedevices, which can be any user interface device, such as a touchsensitive screen, digitized entry pad, etc. The bus also connects adisplay device 5022, such as an LCD screen or monitor, to themicroprocessor 5026 via a display adapter.

The system 5021 may communicate with other computers or networks ofcomputers by way of a network adapter capable of communicating 5028 witha network 5029. Example network adapters are communications channels,token ring, Ethernet or modems. Alternatively, the system 5021 maycommunicate using a wireless interface, such as a CDPD (cellular digitalpacket data) card. The system 5021 may be associated with such othercomputers in a Local Area Network (LAN) or a Wide Area Network (WAN), orthe system 5021 can be a client in a client/server arrangement withanother computer, etc. All of these configurations, as well as theappropriate communications hardware and software, are known in the art.

FIG. 16 illustrates a data processing network 5040 in which one or moreembodiments may be practiced. The data processing network 5040 mayinclude a plurality of individual networks, such as a wireless networkand a wired network, each of which may include a plurality of individualworkstations 5041, 5042, 5043, 5044. Additionally, as those skilled inthe art will appreciate, one or more LANs may be included, where a LANmay comprise a plurality of intelligent workstations coupled to a hostprocessor.

Still referring to FIG. 16, the networks may also include mainframecomputers or servers, such as a gateway computer (client server 5046) orapplication server (remote server 5048 which may access a datarepository and may also be accessed directly from a workstation 5045). Agateway computer 5046 serves as a point of entry into each individualnetwork. A gateway is needed when connecting one networking protocol toanother. The gateway 5046 may be preferably coupled to another network(the Internet 5047 for example) by means of a communications link. Thegateway 5046 may also be directly coupled to one or more workstations5041, 5042, 5043, 5044 using a communications link. The gateway computermay be implemented utilizing an IBM eServer System z server availablefrom International Business Machines Corporation.

Referring concurrently to FIG. 15 and FIG. 16, software programming code5031 which may embody one or more aspects may be accessed by theprocessor 5026 of the system 5020 from long-term storage media 5027,such as a CD-ROM drive or hard drive. The software programming code maybe embodied on any of a variety of known media for use with a dataprocessing system, such as a diskette, hard drive, or CD-ROM. The codemay be distributed on such media, or may be distributed to users 5050,5051 from the memory or storage of one computer system over a network toother computer systems for use by users of such other systems.

Alternatively, the programming code may be embodied in the memory 5025,and accessed by the processor 5026 using the processor bus. Suchprogramming code includes an operating system which controls thefunction and interaction of the various computer components and one ormore application programs 5032. Program code is normally paged fromstorage media 5027 to high-speed memory 5025 where it is available forprocessing by the processor 5026. The techniques and methods forembodying software programming code in memory, on physical media, and/ordistributing software code via networks are well known and will not befurther discussed herein. Program code, when created and stored on atangible medium (including but not limited to electronic memory modules(RAM), flash memory, Compact Discs (CDs), DVDs, Magnetic Tape and thelike is often referred to as a “computer program product”. The computerprogram product medium is typically readable by a processing circuitpreferably in a computer system for execution by the processing circuit.

The cache that is most readily available to the processor (normallyfaster and smaller than other caches of the processor) is the lowest (L1or level one) cache and main store (main memory) is the highest levelcache (L3 if there are 3 levels). The lowest level cache is oftendivided into an instruction cache (I-Cache) holding machine instructionsto be executed and a data cache (D-Cache) holding data operands.

Referring to FIG. 17, an exemplary processor embodiment is depicted forprocessor 5026. Typically one or more levels of cache 5053 are employedto buffer memory blocks in order to improve processor performance. Thecache 5053 is a high speed buffer holding cache lines of memory datathat are likely to be used. Typical cache lines are 64, 128 or 256 bytesof memory data. Separate caches are often employed for cachinginstructions than for caching data. Cache coherence (synchronization ofcopies of lines in memory and the caches) is often provided by various“snoop” algorithms well known in the art. Main memory storage 5025 of aprocessor system is often referred to as a cache. In a processor systemhaving 4 levels of cache 5053, main storage 5025 is sometimes referredto as the level 5 (L5) cache since it is typically faster and only holdsa portion of the non-volatile storage (DASD, tape etc) that is availableto a computer system. Main storage 5025 “caches” pages of data paged inand out of the main storage 5025 by the operating system.

A program counter (instruction counter) 5061 keeps track of the addressof the current instruction to be executed. A program counter in az/Architecture processor is 64 bits and can be truncated to 31 or 24bits to support prior addressing limits. A program counter is typicallyembodied in a PSW (program status word) of a computer such that itpersists during context switching. Thus, a program in progress, having aprogram counter value, may be interrupted by, for example, the operatingsystem (context switch from the program environment to the operatingsystem environment). The PSW of the program maintains the programcounter value while the program is not active, and the program counter(in the PSW) of the operating system is used while the operating systemis executing. Typically, the program counter is incremented by an amountequal to the number of bytes of the current instruction. RISC (ReducedInstruction Set Computing) instructions are typically fixed length whileCISC (Complex Instruction Set Computing) instructions are typicallyvariable length. Instructions of the IBM z/Architecture are CISCinstructions having a length of 2, 4 or 6 bytes. The Program counter5061 is modified by either a context switch operation or a branch takenoperation of a branch instruction for example. In a context switchoperation, the current program counter value is saved in the programstatus word along with other state information about the program beingexecuted (such as condition codes), and a new program counter value isloaded pointing to an instruction of a new program module to beexecuted. A branch taken operation is performed in order to permit theprogram to make decisions or loop within the program by loading theresult of the branch instruction into the program counter 5061.

Typically an instruction fetch unit 5055 is employed to fetchinstructions on behalf of the processor 5026. The fetch unit eitherfetches “next sequential instructions”, target instructions of branchtaken instructions, or first instructions of a program following acontext switch. Modern Instruction fetch units often employ prefetchtechniques to speculatively prefetch instructions based on thelikelihood that the prefetched instructions might be used. For example,a fetch unit may fetch 16 bytes of instruction that includes the nextsequential instruction and additional bytes of further sequentialinstructions.

The fetched instructions are then executed by the processor 5026. In anembodiment, the fetched instruction(s) are passed to a dispatch unit5056 of the fetch unit. The dispatch unit decodes the instruction(s) andforwards information about the decoded instruction(s) to appropriateunits 5057, 5058, 5060. An execution unit 5057 will typically receiveinformation about decoded arithmetic instructions from the instructionfetch unit 5055 and will perform arithmetic operations on operandsaccording to the opcode of the instruction. Operands are provided to theexecution unit 5057 preferably either from memory 5025, architectedregisters 5059 or from an immediate field of the instruction beingexecuted. Results of the execution, when stored, are stored either inmemory 5025, registers 5059 or in other machine hardware (such ascontrol registers, PSW registers and the like).

Virtual addresses are transformed into real addresses using dynamicaddress translation 5062 and, optionally, using access registertranslation 5063.

A processor 5026 typically has one or more units 5057, 5058, 5060 forexecuting the function of the instruction. Referring to FIG. 18A, anexecution unit 5057 may communicate 5071 with architected generalregisters 5059, a decode/dispatch unit 5056, a load store unit 5060, andother 5065 processor units by way of interfacing logic 5071. Anexecution unit 5057 may employ several register circuits 5067, 5068,5069 to hold information that the arithmetic logic unit (ALU) 5066 willoperate on. The ALU performs arithmetic operations such as add,subtract, multiply and divide as well as logical function such as and,or and exclusive-or (XOR), rotate and shift. Preferably the ALU supportsspecialized operations that are design dependent. Other circuits mayprovide other architected facilities 5072 including condition codes andrecovery support logic for example. Typically the result of an ALUoperation is held in an output register circuit 5070 which can forwardthe result to a variety of other processing functions. There are manyarrangements of processor units, the present description is onlyintended to provide a representative understanding of one embodiment.

An ADD instruction for example would be executed in an execution unit5057 having arithmetic and logical functionality while a floating pointinstruction for example would be executed in a floating point executionhaving specialized floating point capability. Preferably, an executionunit operates on operands identified by an instruction by performing anopcode defined function on the operands. For example, an ADD instructionmay be executed by an execution unit 5057 on operands found in tworegisters 5059 identified by register fields of the instruction.

The execution unit 5057 performs the arithmetic addition on two operandsand stores the result in a third operand where the third operand may bea third register or one of the two source registers. The execution unitpreferably utilizes an Arithmetic Logic Unit (ALU) 5066 that is capableof performing a variety of logical functions such as Shift, Rotate, And,Or and XOR as well as a variety of algebraic functions including any ofadd, subtract, multiply, divide. Some ALUs 5066 are designed for scalaroperations and some for floating point. Data may be Big Endian (wherethe least significant byte is at the highest byte address) or LittleEndian (where the least significant byte is at the lowest byte address)depending on architecture. The IBM z/Architecture is Big Endian. Signedfields may be sign and magnitude, 1's complement or 2's complementdepending on architecture. A 2's complement number is advantageous inthat the ALU does not need to design a subtract capability since eithera negative value or a positive value in 2's complement requires only anaddition within the ALU. Numbers are commonly described in shorthand,where a 12 bit field defines an address of a 4,096 byte block and iscommonly described as a 4 Kbyte (Kilo-byte) block, for example.

Referring to FIG. 18B, branch instruction information for executing abranch instruction is typically sent to a branch unit 5058 which oftenemploys a branch prediction algorithm such as a branch history table5082 to predict the outcome of the branch before other conditionaloperations are complete. The target of the current branch instructionwill be fetched and speculatively executed before the conditionaloperations are complete. When the conditional operations are completedthe speculatively executed branch instructions are either completed ordiscarded based on the conditions of the conditional operation and thespeculated outcome. A typical branch instruction may test conditioncodes and branch to a target address if the condition codes meet thebranch requirement of the branch instruction, a target address may becalculated based on several numbers including ones found in registerfields or an immediate field of the instruction for example. The branchunit 5058 may employ an ALU 5074 having a plurality of input registercircuits 5075, 5076, 5077 and an output register circuit 5080. Thebranch unit 5058 may communicate 5081 with general registers 5059,decode dispatch unit 5056 or other circuits 5073, for example.

The execution of a group of instructions can be interrupted for avariety of reasons including a context switch initiated by an operatingsystem, a program exception or error causing a context switch, an I/Ointerruption signal causing a context switch or multi-threading activityof a plurality of programs (in a multi-threaded environment), forexample. Preferably a context switch action saves state informationabout a currently executing program and then loads state informationabout another program being invoked. State information may be saved inhardware registers or in memory for example. State informationpreferably comprises a program counter value pointing to a nextinstruction to be executed, condition codes, memory translationinformation and architected register content. A context switch activitycan be exercised by hardware circuits, application programs, operatingsystem programs or firmware code (microcode, pico-code or licensedinternal code (LIC)) alone or in combination.

A processor accesses operands according to instruction defined methods.The instruction may provide an immediate operand using the value of aportion of the instruction, may provide one or more register fieldsexplicitly pointing to either general purpose registers or specialpurpose registers (floating point registers for example). Theinstruction may utilize implied registers identified by an opcode fieldas operands. The instruction may utilize memory locations for operands.A memory location of an operand may be provided by a register, animmediate field, or a combination of registers and immediate field asexemplified by the z/Architecture long displacement facility wherein theinstruction defines a base register, an index register and an immediatefield (displacement field) that are added together to provide theaddress of the operand in memory for example. Location herein typicallyimplies a location in main memory (main storage) unless otherwiseindicated.

Referring to FIG. 18C, a processor accesses storage using a load/storeunit 5060. The load/store unit 5060 may perform a load operation byobtaining the address of the target operand in memory 5053 and loadingthe operand in a register 5059 or another memory 5053 location, or mayperform a store operation by obtaining the address of the target operandin memory 5053 and storing data obtained from a register 5059 or anothermemory 5053 location in the target operand location in memory 5053. Theload/store unit 5060 may be speculative and may access memory in asequence that is out-of-order relative to instruction sequence, howeverthe load/store unit 5060 is to maintain the appearance to programs thatinstructions were executed in order. A load/store unit 5060 maycommunicate 5084 with general registers 5059, decode/dispatch unit 5056,cache/memory interface 5053 or other elements 5083 and comprises variousregister circuits 5086, 5087, 5088 and 5089, ALUs 5085 and control logic5090 to calculate storage addresses and to provide pipeline sequencingto keep operations in-order. Some operations may be out of order but theload/store unit provides functionality to make the out of orderoperations to appear to the program as having been performed in order,as is well known in the art.

Preferably addresses that an application program “sees” are oftenreferred to as virtual addresses. Virtual addresses are sometimesreferred to as “logical addresses” and “effective addresses”. Thesevirtual addresses are virtual in that they are redirected to physicalmemory location by one of a variety of dynamic address translation (DAT)technologies including, but not limited to, simply prefixing a virtualaddress with an offset value, translating the virtual address via one ormore translation tables, the translation tables preferably comprising atleast a segment table and a page table alone or in combination,preferably, the segment table having an entry pointing to the pagetable. In the z/Architecture, a hierarchy of translation is providedincluding a region first table, a region second table, a region thirdtable, a segment table and an optional page table. The performance ofthe address translation is often improved by utilizing a translationlookaside buffer (TLB) which comprises entries mapping a virtual addressto an associated physical memory location. The entries are created whenthe DAT translates a virtual address using the translation tables.Subsequent use of the virtual address can then utilize the entry of thefast TLB rather than the slow sequential translation table accesses. TLBcontent may be managed by a variety of replacement algorithms includingLRU (Least Recently used).

In the case where the processor is a processor of a multi-processorsystem, each processor has responsibility to keep shared resources, suchas I/O, caches, TLBs and memory, interlocked for coherency. Typically,“snoop” technologies will be utilized in maintaining cache coherency. Ina snoop environment, each cache line may be marked as being in any oneof a shared state, an exclusive state, a changed state, an invalid stateand the like in order to facilitate sharing.

I/O units 5054 (FIG. 17) provide the processor with means for attachingto peripheral devices including tape, disc, printers, displays, andnetworks for example. I/O units are often presented to the computerprogram by software drivers. In mainframes, such as the System z fromIBM, channel adapters and open system adapters are I/O units of themainframe that provide the communications between the operating systemand peripheral devices.

Further, other types of computing environments can benefit from one ormore aspects. As an example, an environment may include an emulator(e.g., software or other emulation mechanisms), in which a particulararchitecture (including, for instance, instruction execution,architected functions, such as address translation, and architectedregisters) or a subset thereof is emulated (e.g., on a native computersystem having a processor and memory). In such an environment, one ormore emulation functions of the emulator can implement one or moreembodiments, even though a computer executing the emulator may have adifferent architecture than the capabilities being emulated. As oneexample, in emulation mode, the specific instruction or operation beingemulated is decoded, and an appropriate emulation function is built toimplement the individual instruction or operation.

In an emulation environment, a host computer includes, for instance, amemory to store instructions and data; an instruction fetch unit tofetch instructions from memory and to optionally, provide localbuffering for the fetched instruction; an instruction decode unit toreceive the fetched instructions and to determine the type ofinstructions that have been fetched; and an instruction execution unitto execute the instructions. Execution may include loading data into aregister from memory; storing data back to memory from a register; orperforming some type of arithmetic or logical operation, as determinedby the decode unit. In one example, each unit is implemented insoftware. For instance, the operations being performed by the units areimplemented as one or more subroutines within emulator software.

More particularly, in a mainframe, architected machine instructions areused by programmers, usually today “C” programmers, often by way of acompiler application. These instructions stored in the storage mediummay be executed natively in a z/Architecture IBM® Server, oralternatively in machines executing other architectures. They can beemulated in the existing and in future IBM® mainframe servers and onother machines of IBM® (e.g., Power Systems servers and System xServers). They can be executed in machines running Linux on a widevariety of machines using hardware manufactured by IBM®, Intel®, AMD,and others. Besides execution on that hardware under z/Architecture,Linux can be used as well as machines which use emulation by Hercules,UMX, or FSI (Fundamental Software, Inc), where generally execution is inan emulation mode. In emulation mode, emulation software is executed bya native processor to emulate the architecture of an emulated processor.

The native processor typically executes emulation software comprisingeither firmware or a native operating system to perform emulation of theemulated processor. The emulation software is responsible for fetchingand executing instructions of the emulated processor architecture. Theemulation software maintains an emulated program counter to keep trackof instruction boundaries. The emulation software may fetch one or moreemulated machine instructions at a time and convert the one or moreemulated machine instructions to a corresponding group of native machineinstructions for execution by the native processor. These convertedinstructions may be cached such that a faster conversion can beaccomplished. Notwithstanding, the emulation software is to maintain thearchitecture rules of the emulated processor architecture so as toassure operating systems and applications written for the emulatedprocessor operate correctly. Furthermore, the emulation software is toprovide resources identified by the emulated processor architectureincluding, but not limited to, control registers, general purposeregisters, floating point registers, dynamic address translationfunction including segment tables and page tables for example, interruptmechanisms, context switch mechanisms, Time of Day (TOD) clocks andarchitected interfaces to I/O subsystems such that an operating systemor an application program designed to run on the emulated processor, canbe run on the native processor having the emulation software.

A specific instruction being emulated is decoded, and a subroutine iscalled to perform the function of the individual instruction. Anemulation software function emulating a function of an emulatedprocessor is implemented, for example, in a “C” subroutine or driver, orsome other method of providing a driver for the specific hardware aswill be within the skill of those in the art after understanding thedescription of the preferred embodiment. Various software and hardwareemulation patents including, but not limited to U.S. Pat. No. 5,551,013,entitled “Multiprocessor for Hardware Emulation”, by Beausoleil et al.;and U.S. Pat. No. 6,009,261, entitled “Preprocessing of Stored TargetRoutines for Emulating Incompatible Instructions on a Target Processor”,by Scalzi et al; and U.S. Pat. No. 5,574,873, entitled “Decoding GuestInstruction to Directly Access Emulation Routines that Emulate the GuestInstructions”, by Davidian et al; and U.S. Pat. No. 6,308,255, entitled“Symmetrical Multiprocessing Bus and Chipset Used for CoprocessorSupport Allowing Non-Native Code to Run in a System”, by Gorishek et al;and U.S. Pat. No. 6,463,582, entitled “Dynamic Optimizing Object CodeTranslator for Architecture Emulation and Dynamic Optimizing Object CodeTranslation Method”, by Lethin et al; and U.S. Pat. No. 5,790,825,entitled “Method for Emulating Guest Instructions on a Host ComputerThrough Dynamic Recompilation of Host Instructions”, by Eric Traut, eachof which is hereby incorporated by reference herein in its entirety; andmany others, illustrate a variety of known ways to achieve emulation ofan instruction format architected for a different machine for a targetmachine available to those skilled in the art.

In FIG. 19, an example of an emulated host computer system 5092 isprovided that emulates a host computer system 5000′ of a hostarchitecture. In the emulated host computer system 5092, the hostprocessor (CPU) 5091 is an emulated host processor (or virtual hostprocessor) and comprises an emulation processor 5093 having a differentnative instruction set architecture than that of the processor 5091 ofthe host computer 5000′. The emulated host computer system 5092 hasmemory 5094 accessible to the emulation processor 5093. In the exampleembodiment, the memory 5094 is partitioned into a host computer memory5096 portion and an emulation routines 5097 portion. The host computermemory 5096 is available to programs of the emulated host computer 5092according to host computer architecture. The emulation processor 5093executes native instructions of an architected instruction set of anarchitecture other than that of the emulated processor 5091, the nativeinstructions obtained from emulation routines memory 5097, and mayaccess a host instruction for execution from a program in host computermemory 5096 by employing one or more instruction(s) obtained in asequence & access/decode routine which may decode the hostinstruction(s) accessed to determine a native instruction executionroutine for emulating the function of the host instruction accessed.Other facilities that are defined for the host computer system 5000′architecture may be emulated by architected facilities routines,including such facilities as general purpose registers, controlregisters, dynamic address translation and I/O subsystem support andprocessor cache, for example. The emulation routines may also takeadvantage of functions available in the emulation processor 5093 (suchas general registers and dynamic translation of virtual addresses) toimprove performance of the emulation routines. Special hardware andoff-load engines may also be provided to assist the processor 5093 inemulating the function of the host computer 5000′.

In a further embodiment, one or more aspects relate to cloud computing.It is understood in advance that although this disclosure includes adetailed description on cloud computing, implementation of the teachingsrecited herein are not limited to a cloud computing environment. Rather,embodiments of the present invention are capable of being implemented inconjunction with any other type of computing environment now known orlater developed.

Cloud computing is a model of service delivery for enabling convenient,on-demand network access to a shared pool of configurable computingresources (e.g. networks, network bandwidth, servers, processing,memory, storage, applications, virtual machines, and services) that canbe rapidly provisioned and released with minimal management effort orinteraction with a provider of the service. This cloud model may includeat least five characteristics, at least three service models, and atleast four deployment models.

Characteristics are as follows:

On-demand self-service: a cloud consumer can unilaterally provisioncomputing capabilities, such as server time and network storage, asneeded automatically without requiring human interaction with theservice's provider.

Broad network access: capabilities are available over a network andaccessed through standard mechanisms that promote use by heterogeneousthin or thick client platforms (e.g., mobile phones, laptops, and PDAs).

Resource pooling: the provider's computing resources are pooled to servemultiple consumers using a multi-tenant model, with different physicaland virtual resources dynamically assigned and reassigned according todemand. There is a sense of location independence in that the consumergenerally has no control or knowledge over the exact location of theprovided resources but may be able to specify location at a higher levelof abstraction (e.g., country, state, or datacenter).

Rapid elasticity: capabilities can be rapidly and elasticallyprovisioned, in some cases automatically, to quickly scale out andrapidly released to quickly scale in. To the consumer, the capabilitiesavailable for provisioning often appear to be unlimited and can bepurchased in any quantity at any time.

Measured service: cloud systems automatically control and optimizeresource use by leveraging a metering capability at some level ofabstraction appropriate to the type of service (e.g., storage,processing, bandwidth, and active user accounts). Resource usage can bemonitored, controlled, and reported providing transparency for both theprovider and consumer of the utilized service.

Service Models are as follows:

Software as a Service (SaaS): the capability provided to the consumer isto use the provider's applications running on a cloud infrastructure.The applications are accessible from various client devices through athin client interface such as a web browser (e.g., web-based email). Theconsumer does not manage or control the underlying cloud infrastructureincluding network, servers, operating systems, storage, or evenindividual application capabilities, with the possible exception oflimited user-specific application configuration settings.

Platform as a Service (PaaS): the capability provided to the consumer isto deploy onto the cloud infrastructure consumer-created or acquiredapplications created using programming languages and tools supported bythe provider. The consumer does not manage or control the underlyingcloud infrastructure including networks, servers, operating systems, orstorage, but has control over the deployed applications and possiblyapplication hosting environment configurations.

Infrastructure as a Service (IaaS): the capability provided to theconsumer is to provision processing, storage, networks, and otherfundamental computing resources where the consumer is able to deploy andrun arbitrary software, which can include operating systems andapplications. The consumer does not manage or control the underlyingcloud infrastructure but has control over operating systems, storage,deployed applications, and possibly limited control of select networkingcomponents (e.g., host firewalls).

Deployment Models are as follows:

Private cloud: the cloud infrastructure is operated solely for anorganization. It may be managed by the organization or a third party andmay exist on-premises or off-premises.

Community cloud: the cloud infrastructure is shared by severalorganizations and supports a specific community that has shared concerns(e.g., mission, security requirements, policy, and complianceconsiderations). It may be managed by the organizations or a third partyand may exist on-premises or off-premises.

Public cloud: the cloud infrastructure is made available to the generalpublic or a large industry group and is owned by an organization sellingcloud services.

Hybrid cloud: the cloud infrastructure is a composition of two or moreclouds (private, community, or public) that remain unique entities butare bound together by standardized or proprietary technology thatenables data and application portability (e.g., cloud bursting forloadbalancing between clouds).

A cloud computing environment is service oriented with a focus onstatelessness, low coupling, modularity, and semantic interoperability.At the heart of cloud computing is an infrastructure comprising anetwork of interconnected nodes.

Referring now to FIG. 20, a schematic of an example of a cloud computingnode is shown. Cloud computing node 6010 is only one example of asuitable cloud computing node and is not intended to suggest anylimitation as to the scope of use or functionality of embodiments of theinvention described herein. Regardless, cloud computing node 6010 iscapable of being implemented and/or performing any of the functionalityset forth hereinabove.

In cloud computing node 6010 there is a computer system/server 6012,which is operational with numerous other general purpose or specialpurpose computing system environments or configurations. Examples ofwell-known computing systems, environments, and/or configurations thatmay be suitable for use with computer system/server 6012 include, butare not limited to, personal computer systems, server computer systems,thin clients, thick clients, handheld or laptop devices, multiprocessorsystems, microprocessor-based systems, set top boxes, programmableconsumer electronics, network PCs, minicomputer systems, mainframecomputer systems, and distributed cloud computing environments thatinclude any of the above systems or devices, and the like.

Computer system/server 6012 may be described in the general context ofcomputer system executable instructions, such as program modules, beingexecuted by a computer system. Generally, program modules may includeroutines, programs, objects, components, logic, data structures, and soon that perform particular tasks or implement particular abstract datatypes. Computer system/server 6012 may be practiced in distributed cloudcomputing environments where tasks are performed by remote processingdevices that are linked through a communications network. In adistributed cloud computing environment, program modules may be locatedin both local and remote computer system storage media including memorystorage devices.

As shown in FIG. 20, computer system/server 6012 in cloud computing node6010 is shown in the form of a general-purpose computing device. Thecomponents of computer system/server 6012 may include, but are notlimited to, one or more processors or processing units 6016, a systemmemory 6028, and a bus 6018 that couples various system componentsincluding system memory 6028 to processor 6016.

Bus 6018 represents one or more of any of several types of busstructures, including a memory bus or memory controller, a peripheralbus, an accelerated graphics port, and a processor or local bus usingany of a variety of bus architectures. By way of example, and notlimitation, such architectures include Industry Standard Architecture(ISA) bus, Micro Channel Architecture (MCA) bus, Enhanced ISA (EISA)bus, Video Electronics Standards Association (VESA) local bus, andPeripheral Component Interconnect (PCI) bus.

Computer system/server 6012 typically includes a variety of computersystem readable media. Such media may be any available media that isaccessible by computer system/server 6012, and it includes both volatileand non-volatile media, removable and non-removable media.

System memory 6028 can include computer system readable media in theform of volatile memory, such as random access memory (RAM) 6030 and/orcache memory 6032. Computer system/server 6012 may further include otherremovable/non-removable, volatile/non-volatile computer system storagemedia. By way of example only, storage system 6034 can be provided forreading from and writing to a non-removable, non-volatile magnetic media(not shown and typically called a “hard drive”). Although not shown, amagnetic disk drive for reading from and writing to a removable,non-volatile magnetic disk (e.g., a “floppy disk”), and an optical diskdrive for reading from or writing to a removable, non-volatile opticaldisk such as a CD-ROM, DVD-ROM or other optical media can be provided.In such instances, each can be connected to bus 6018 by one or more datamedia interfaces. As will be further depicted and described below,memory 6028 may include at least one program product having a set (e.g.,at least one) of program modules that are configured to carry out thefunctions of embodiments of the invention.

Program/utility 6040, having a set (at least one) of program modules6042, may be stored in memory 6028 by way of example, and notlimitation, as well as an operating system, one or more applicationprograms, other program modules, and program data. Each of the operatingsystem, one or more application programs, other program modules, andprogram data or some combination thereof, may include an implementationof a networking environment. Program modules 6042 generally carry outthe functions and/or methodologies of embodiments of the invention asdescribed herein.

Computer system/server 6012 may also communicate with one or moreexternal devices 6014 such as a keyboard, a pointing device, a display6024, etc.; one or more devices that enable a user to interact withcomputer system/server 6012; and/or any devices (e.g., network card,modem, etc.) that enable computer system/server 6012 to communicate withone or more other computing devices. Such communication can occur viaInput/Output (I/O) interfaces 6022. Still yet, computer system/server6012 can communicate with one or more networks such as a local areanetwork (LAN), a general wide area network (WAN), and/or a publicnetwork (e.g., the Internet) via network adapter 6020. As depicted,network adapter 6020 communicates with the other components of computersystem/server 6012 via bus 6018. It should be understood that althoughnot shown, other hardware and/or software components could be used inconjunction with computer system/server 6012. Examples, include, but arenot limited to: microcode, device drivers, redundant processing units,external disk drive arrays, RAID systems, tape drives, and data archivalstorage systems, etc.

Referring now to FIG. 21, illustrative cloud computing environment 6050is depicted. As shown, cloud computing environment 6050 comprises one ormore cloud computing nodes 6010 with which local computing devices usedby cloud consumers, such as, for example, personal digital assistant(PDA) or cellular telephone 6054A, desktop computer 6054B, laptopcomputer 6054C, and/or automobile computer system 6054N may communicate.Nodes 6010 may communicate with one another. They may be grouped (notshown) physically or virtually, in one or more networks, such asPrivate, Community, Public, or Hybrid clouds as described hereinabove,or a combination thereof. This allows cloud computing environment 6050to offer infrastructure, platforms and/or software as services for whicha cloud consumer does not need to maintain resources on a localcomputing device. It is understood that the types of computing devices6054A-N shown in FIG. 21 are intended to be illustrative only and thatcomputing nodes 6010 and cloud computing environment 6050 cancommunicate with any type of computerized device over any type ofnetwork and/or network addressable connection (e.g., using a webbrowser).

Referring now to FIG. 22, a set of functional abstraction layersprovided by cloud computing environment 6050 (FIG. 21) is shown. Itshould be understood in advance that the components, layers, andfunctions shown in FIG. 22 are intended to be illustrative only andembodiments of the invention are not limited thereto. As depicted, thefollowing layers and corresponding functions are provided:

Hardware and software layer 6060 includes hardware and softwarecomponents. Examples of hardware components include mainframes, in oneexample IBM® zSeries® systems; RISC (Reduced Instruction Set Computer)architecture based servers, in one example IBM pSeries® systems; IBMxSeries® systems; IBM BladeCenter systems; storage devices; networks andnetworking components. Examples of software components include networkapplication server software, in one example IBM WebSphere® applicationserver software; and database software, in one example IBM DB2® databasesoftware. (IBM, zSeries, pSeries, xSeries, BladeCenter, WebSphere, andDB2 are trademarks of International Business Machines Corporationregistered in many jurisdictions worldwide).

Virtualization layer 6062 provides an abstraction layer from which thefollowing examples of virtual entities may be provided: virtual servers;virtual storage; virtual networks, including virtual private networks;virtual applications and operating systems; and virtual clients.

In one example, management layer 6064 may provide the functionsdescribed below. Resource provisioning provides dynamic procurement ofcomputing resources and other resources that are utilized to performtasks within the cloud computing environment. Metering and Pricingprovide cost tracking as resources are utilized within the cloudcomputing environment, and billing or invoicing for consumption of theseresources. In one example, these resources may comprise applicationsoftware licenses. Security provides identity verification for cloudconsumers and tasks, as well as protection for data and other resources.User portal provides access to the cloud computing environment forconsumers and system administrators. Service level management providescloud computing resource allocation and management such that requiredservice levels are met. Service Level Agreement (SLA) planning andfulfillment provide pre-arrangement for, and procurement of, cloudcomputing resources for which a future requirement is anticipated inaccordance with an SLA.

Workloads layer 6066 provides examples of functionality for which thecloud computing environment may be utilized. Examples of workloads andfunctions which may be provided from this layer include: mapping andnavigation; software development and lifecycle management; virtualclassroom education delivery; data analytics processing; and transactionprocessing.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a”, “an” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. It willbe further understood that the terms “comprises” and/or “comprising”,when used in this specification, specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below, if any, areintended to include any structure, material, or act for performing thefunction in combination with other claimed elements as specificallyclaimed. The description of one or more embodiments has been presentedfor purposes of illustration and description, but is not intended to beexhaustive or limited to in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the art. Theembodiment was chosen and described in order to best explain variousaspects and the practical application, and to enable others of ordinaryskill in the art to understand various embodiments with variousmodifications as are suited to the particular use contemplated.

What is claimed is:
 1. A computer program product for reconfiguring acomputing environment, said computer program product comprising: atleast one computer readable storage medium readable by at least oneprocessing circuit and storing instructions for performing a methodcomprising: determining that a configuration architectural mode facilityis installed in a computing environment that is configured for aplurality of architectural modes and has a defined power-on sequencethat is to power-on the computing environment in one architectural modeof the plurality of architectural modes, the one architectural modecomprising a first instruction set architecture and having a first setof supported features; based on determining that the configurationarchitectural mode facility is installed, reconfiguring the computingenvironment to restrict use of the one architectural mode, wherein thereconfiguring comprises: selecting a different power-on sequence topower-on the computing environment in another architectural mode of theplurality of architectural modes, wherein the other architectural modeis different from the one architectural mode, and the otherarchitectural mode comprises a second instruction set architecture andhas a second set of supported features; and executing the differentpower-on sequence to power-on the computing environment in the otherarchitectural mode in place of the one architectural mode restrictinguse of the one architectural mode, wherein the executing the differentpower-on sequence comprises creating a new program status word tocontrol operations of the computing environment in the otherarchitectural mode, the creating the new program status word comprisingforming the new program status word to have a format indicated by theother architectural mode.
 2. The computer program product of claim 1,wherein the creating the new program status word comprises inverting anarchitectural mode indicator in the new program status word to indicatethe other architectural mode.
 3. The computer program product of claim1, wherein the determining that the configuration architectural modefacility is installed comprises checking a facility indicator.
 4. Thecomputer program product of claim 1, wherein the reconfiguring furthercomprises disabling within the computing environment one or moreoperations to support the one architectural mode, the one or moreoperations comprising a switch operation to switch from the otherarchitectural mode to the one architectural mode, wherein a switch backto the one architectural mode is disabled.
 5. The computer programproduct of claim 4, wherein the disabling comprises altering processingof a signal processor instruction to provide an error based on a requestto switch back to the one architectural mode.
 6. The computer programproduct of claim 1, wherein the method further comprises performing areset of at least one processor of the computing environment, whereinthe performing the reset comprises: resetting the computing environmentin the other architectural mode, the resetting comprising setting anarchitectural mode of the computing environment to the otherarchitectural mode; and inverting an architectural mode indicator in aprogram status word to indicate the other architectural mode.
 7. Thecomputer program product of claim 1, wherein the reconfiguring compriseschanging processing of a signal processor operation, wherein a signalprocessor operation to set an architectural mode of the computingenvironment to the architectural mode it is currently in results instoring status indicating the computing environment is currently in thearchitectural mode, this status being treated as acceptable by an issuerof the signal processor operation.
 8. The computer program product ofclaim 1, wherein the one architectural mode is a legacy mode and theother architectural mode is an enhanced mode, and wherein the first setof supported features comprise 31-bit addressing and use of 32-bitgeneral purpose registers, and the second set of supported featurescomprises 64-bit addressing and use of 64-bit general purpose registers.9. The computer program product of claim 1, wherein the computingenvironment is a virtual guest environment having a host processor, afirst guest virtual machine at a first level of virtualization, and asecond guest virtual machine at a second level of virtualization, andwherein the reconfiguring is performed for the host processor and thefirst guest virtual machine, but not for the second guest virtualmachine, the second guest virtual machine being initiated and processingin the one architectural mode.
 10. A computer system for reconfiguring acomputing environment, said computer system comprising: a memory; and aprocessor in communication with the memory, wherein the computer systemis configured to perform a method, said method comprising: determiningthat a configuration architectural mode facility is installed in acomputing environment that is configured for a plurality ofarchitectural modes and has a defined power-on sequence that is topower-on the computing environment in one architectural mode of theplurality of architectural modes, the one architectural mode comprisinga first instruction set architecture and having a first set of supportedfeatures; based on determining that the configuration architectural modefacility is installed, reconfiguring, by the processor, the computingenvironment to restrict use of the one architectural mode, wherein thereconfiguring comprises: selecting a different power-on sequence topower-on the computing environment in another architectural mode of theplurality of architectural modes, wherein the other architectural modeis different from the one architectural mode, and the otherarchitectural mode comprises a second instruction set architecture andhas a second set of supported features; and executing the differentpower-on sequence to power-on the computing environment in the otherarchitectural mode in place of the one architectural mode restrictinguse of the one architectural mode, wherein the executing the differentpower-on sequence comprises creating a new program status word tocontrol operations of the computing environment in the otherarchitectural mode, the creating the new program status word comprisingforming the new program status word to have a format indicated by theother architectural mode.
 11. The computer system of claim 10, whereinthe creating the new program status word comprises inverting anarchitectural mode indicator in the new program status word to indicatethe other architectural mode.
 12. The computer system of claim 10,wherein the determining that the configuration architectural modefacility is installed comprises checking a facility indicator.
 13. Thecomputer system of claim 10, wherein the reconfiguring further comprisesdisabling within the computing environment one or more operations tosupport the one architectural mode, the one or more operationscomprising a switch operation to switch from the other architecturalmode to the one architectural mode, wherein a switch back to the onearchitectural mode is disabled.
 14. The computer system of claim 13,wherein the disabling comprises altering processing of a signalprocessor instruction to provide an error based on a request to switchback to the one architectural mode.
 15. The computer system of claim 10,wherein the method further comprises performing a reset of at least oneprocessor of the computing environment, wherein the performing the resetcomprises: resetting the computing environment in the otherarchitectural mode, the resetting comprising setting an architecturalmode of the computing environment to the other architectural mode; andinverting an architectural mode indicator in a program status word toindicate the other architectural mode.
 16. The computer system of claim10, wherein the reconfiguring comprises changing processing of a signalprocessor operation, wherein a signal processor operation to set anarchitectural mode of the computing environment to the architecturalmode it is currently in results in storing status indicating thecomputing environment is currently in the architectural mode, thisstatus being treated as acceptable by an issuer of the signal processoroperation.
 17. The computer system of claim 10, wherein the onearchitectural mode is a legacy mode and the other architectural mode isan enhanced mode, and wherein the first set of supported featurescomprise 31-bit addressing and use of 32-bit general purpose registers,and the second set of supported features comprises 64-bit addressing anduse of 64-bit general purpose registers.
 18. The computer system ofclaim 10, wherein the computing environment is a virtual guestenvironment having a host processor, a first guest virtual machine at afirst level of virtualization, and a second guest virtual machine at asecond level of virtualization, and wherein the reconfiguring isperformed for the host processor and the first guest virtual machine,but not for the second guest virtual machine, the second guest virtualmachine being initiated and processing in the one architectural mode.19. A computer program product for configuring a computing environment,said computer program product comprising: at least one computer readablestorage medium readable by at least one processing circuit and storinginstructions for performing a method comprising: configuring a computingenvironment to perform operations in a selected architectural mode, theconfiguring comprising: commencing initialization of the computingenvironment using a stored program status word, the stored programstatus word having a format of an architectural mode different from theselected architectural mode; determining that the stored program statusword has the format of the architectural mode different from theselected architectural mode; based on determining that the storedprogram status word has the format of the architectural mode differentfrom the selected architectural mode, automatically modifying the storedprogram status word to have a format of the selected architectural mode,the automatically modifying being performed absent an explicit requestto switch to the selected architectural mode; and completinginitialization of the computing environment using the modified programstatus word having the format of the selected architectural mode toconfigure the computing environment in the selected architectural mode.